The New York Herald Newspaper, September 16, 1876, Page 3

5 TAULETT'S PONT RULE. | Progress in the Art of Excavating Under Water. TRIOMPHS OVER GREAT DIFFICULTIES. | The Thames Tunnel and the Cornish Tin Miucs in England. SUCCESSFUL ENGINEERING IN AMERICA. Chicago Tunnel and the Blossom Rock in, San‘ Francisco Bay. HELL GATE WORKS, History of the Undertaking and Its Progress Toward Completion, ‘The near approach of the day fixed on for the great Dlast at Hell Gate, Kast River, creates a vast amount of speculation regarding that grand work, and the re- sults likely to arise from its successful completion, The operations being entirely new to engineering Bclence, their progress has been watched with the greatest interest by engincers, because their success will be the solution of many a vexed problem in the Improvement of our rivers and harbors, In order to form a proper idea of the magnitude and importance of the work at Hallett’s Point reef, it is necessary to briefly review the history of subaqueous mining from its introduction down to our own time, and compare the results obtained as the art advancod from erudity to almost perfection. Progress in the art of mining bas been marked by ita most important advances since the Invention of gunpowder as a chief agent, Previously very few mining works of any importance were executea be- cause of the great difficulty experienced in excavating the solid formations that present themselves when such operations are carried out on a large scale. When wo come to calculate the enormous labor that was nec- essary to dig out tbe great biocks of stone which now form the objects of wonder in tho massive walls of Qncient ruins we are filled with admiration at the in- genuity, skill and perseverance of those carly engi- neers, who succeeded in overcoming almost insu- perable difficulties in procuring their materi ANCIENT EXCAVATIONS, There is nodoubt that the builders of such struc- tures as the Babylonian temples and the great’ pyra- mids of Cheops used the wedge principally in separat- ing the big blocks from their original rock beds, It is Probable that when the masses of stone wero selected for excavation’ holes Were drilled close together along the lines marking their outlines, and, with their directions, as nearly as possible, “ coincident with the plane of natural cleavage. These were subsequently united, us it were, by a system of oblique drilling which pierced the septi dividing the original holes, and thus the adheston of the block to its original formation was retiuced to a minimum, Now the wedges were introduced into the cults so fornied and their action soon ruptured the small con- necting pieces of rock, and the block was completely detached from its quarry bed. Such operations en- failed !mmonse labor, and tho time consumed must ave been also very great, but as the works were usu- ally, it might be said invariably, performed by slaves pnd prisoners of war, the former consideration counted for luttie in the estimation of rulers ambitious of erect- ing imperishable monuments, and the latter was nade ‘up for by the numbers of the workmen. This system evidently prevailed until the adoption of gunpowder mining agent and was improved only by the ad- ‘vances made in the art of tempering mining tools and fn the facilities for applying them to the work in hand. It is believed by some writers that the aid of powerful acids wag called in by the carly miners to assist in dis integrating the points of adhesion between the blocks and their parent formations, but this view is unimpor- fant except as a point of detail in considering the main question of ancient mining. THR EARLY USE OF POWDER was entirely confined to artillery and military mining. When the primitive gun was first used as a breaching arm at the sieges of Constantinople and Rhodes the destruction of the wail defences was invariably fol- lowed by open assaults, and the defence was limited to the erection of obstructions in the breach and such other means of delaying the advance of the enemy as the military skill and experience of the detenders could suggest. Ata later stage of the progress of the mill- tary art mines were ased for the destruction as well as the defence of walls and bridges, and a system of ex- cavated approaches, intreochments and other expedi- ents in engineering tactics adopted which has been developed into the present practice. Nearly all these operations necessitated the extensive use of powder as an explosive agent, and from tho success which attended its application we have the mine de pro- jection or bombshell in its many forms, as well as those terrible plans of attack which have been so fearfully Wostratea during recent wars and particularly in the famous assault on the Confederate lines at Peters- burg, whereby a large section of the defensive works was liftea bodily in the air and scattered with its de- fenders py the explosion of a great military mine. Bat it is of the uses of explosives in the operations of civil engineering that our present article is designed to treat, and more particularly of their application to the purposes of SUBAQUROUS EXCAVATIONS, MINING, ZUNNRLLING, and other similar undertakings for the benefit of com- merce and navigation, the chief object being to tilus- trate the great difficulties, dangers and advantages at- tending such works and the principles of modern en- gineering, which we believe are about to be successful At the Hell Gate works on tho East River at New York pity. A brief review of the principal works which are prop. arly classed under the above head will be interesting to the reader, as it will inform him as to the progress of this important branch of engineering and how each auccess prepared the way for that immediately follow- Ing it, Inthe interests of the common weal men are tontinually striving to solve the problems presented by patare, or, to speak more correctly, are endeavoring to Adapt nataral conditions to human necessities, Thus we select a favorable site for a city on a sheltered island bear the sen or on a well jocated bund of ono of our Frent rivers. ‘The selection ts made because of the general advantages of the location with roference to prospective commercial manufacturing interests, and ag the settlement increases in importance the inbab- Ikants proceed to remove local difficulties which would of themselves tend to impair the future prospects of the city by limiting its growth and im. peding its development. We deepen chan- gels, fill up swamps, cut down hills enclose wud banks, remove sunken rocks, perforate moun- lains with tunnels, and construct roadways over broad rivers by bridges, or under them by subaqueus tannels, vnts) the original aspects of the place dis Appear under'the artiticm! features which the busy hands of man mouid on the face of nature. GREAT TRICMPHS OVER MATERIAL OBSTACLES have rewarded human enterprise witllin the last con- tary, which may be called the first of the aze of labor. ‘The application of steam as a great motor has revolu- tonized the world, ang bas created yecessities which were never felt prior to the days of tho incomo- hive and the ocean steamship. Man’s ideas have been expanded ia proportion to the knowledge he gains of the world he lives on, and the word ‘impossible’ bas beeo replaced by that ef -‘nexpedient” when the execution Of any project im deterred on ac- count of apparent difficulty. This idea filled the mind of the first Napoleon when he discussed with the Enghsb statesman Fox the project for an inierna- | tional tunnel under the Straits of Dover, A warm ad- mirer of bis companion the Emperor gleefully ro- marked :—"Oh! clest une des grandes choses que nous powrrons faire ensemble'’'—O! it 18 one of the great things that we will do together, He never considered the dificuities of the uudertaking, regarding themas EE _———_ _ a NEW YORK HERALD, SATURDAY, SEPTEMBER 16, 1876.-WITH SUPPLEMENT. surmountable by the skilland the daring of the en- giveers of France and England, and enjoyod in antici- pation the glory that would accrue to himself and bia friend Fox from the success of the great work. THE THAMES TUNKEL. Brunel unhesitatingly grappled with the problem of tunnelling under the River Thames and solved it triumphantly in the face of immense difficulties and inoxperience in such undertakings, The line extended from Rotberhithe té Wapping, a distance of about 1,200 feet, and passed through borizontal strata which, from the fact that they immediately underlay the river, were subject to variations of pressure created by the tidal movements) The work was com- menced im 1825, and after overcoming many difficulties and the effect of several casualtics was sac- cessfully completed in 184%. Although aptil re- cently the Thames tunnel could not be classed as a work of great utility, still the experience gained in its construction has mainly contributed to the success of other works of the same character, and as a great ex- periment in subaqueous tunnelling 1t must be regarded as one of the most important undertakings of the age, TUR CORNISH MIXES. Although prosecuted in tbdordinary work of min- ing the great submarine workings of the Cornish mines, which extend for considerabie distances under the sea, must be regarded as among the most splendid uchievements of modern engineering. Far beneath the rolling billows of the Irish Sea, undisturbed by whe howling storms that lash this iron-bound coast with in- describable fury, and buried far below the ocean graves of the shipwrecked saliors, the miner, pick in band, delves among the mineral trens- ures that have lain for myriads of ages in the bowels of the earth and sends them to the upper world to play their purt in the various branches of human industry. The ocean itself bas thus proved to be an insufficient barrier to the aggressiveness of wealth- seeking man, and the success which has attended his | efforts under such extraordinary opposing conditions | encourages us in the belief that we are but opening the | treasury of nature and that all her wonderful wealth is a8 yet comparatively untouched. These submarine excavations also show the feasibility of similar works conducted on the grandest scale, and we must regard as among the possibilities of the future a grand system of subaqueous communication between countries now separated by considerable expanses of water. THE TUNNEL UNDER LAKE MICHIGAN aT CHICAGO, A smalley but no less remarkable feat of subaqueous tunnelling has been accomplished by American engt- neers in the construction of the lake supply tunnel of the Chicago Waterworks, This work 1s perfectly uniqu nd its prosecution was surrounded with difll- culties that have not been met on any preceding work. ‘The object being to introduce @ supply of pure water from Lake Michigan into the city of Chicago from a part of the lake which was uppolluted by the drainago of such a large city, it became necessary to tunnel out under the bed of the lake for a distance of some two miles, and connect the subaqueous aqueduct with a water tower erected in the lake, from which the pure ele- ment would flow into the conduit and so to the city. Such was the plan and so it bas been executed, and Chicago is vow supplicd with pure water from an inexhaustible reservoir, which covers an area of 22,400 square miles, Horo we bave another example of success in subaqueous tunnelling which challenges the admiration of the world and sets men thinking how the same results can be produced elsewhere. There is scarcely a limit to be placed to the engineering possibilities of the coming cenvury when We come to consider the strides that have been mado in this one. Tho data and experience gathered in the ex- ecution of the great works we bave barely mentioned aro suMcient to warrant any project like that of the Channel Tunnel or the railroad subway under tho Hudson River. We see no reason why the Niagara River cannot bo tunnelied a few miles above the Falls, for it will probably take many centuries beforo tho great river ean eat its way backward such a distance, and m the meantime science will have provided a simpler means of communication across the foaming waters of the Upper-St. Lawrence. ‘The application of the principles of subaqueous tun- nelling to the removal of rocks that obstruct chann and render navigation dangerous in any harbor brings us to the review oT the recent REMOVAL OF THE BLOSSOM ROCK in San Francisco Bay, California, and other similar ob- structions in our own harbor; brings us to tho con- sideration of another bravch of subaqueous mining which bas assumed enormous importance in the work ot clearing our harbors {fim dangerous rocks, reefs and other dangers to navigation. The operations exc- cuted in the removal of the Blossom Rock were tho first trials of the new system of internal working, as distinct from the ordinary or external plan which had hitherto been followed in such cases. It must be re- garded as the pioneer work of its kind, and has been attended with the fullest measure of success. f According to the accounts given of this undertaking by those engaged in the mining oporations the top of the rock was about five feet below the level of low water, mean tide, and at the depth of twenty-four fect was presented an area measuring 195 feet long by 105 fect wide, the shape being elliptical, The estimated cubic contents of the mass within the above lines of measuro- ment was about 5,000 cubic yards, and the geological character of the rock was that of metamorphic sand- stone in irregular strata. This term metamorphic, when applied in a geological sense, indicates that the formation was originally of the aqueous class, but by the subsequent action of subterranean heat became changed into a semi-igneaus state, in which the origi- nai stratification 18 preserved, but the constituent par- ticles have assumed a variety of crystalline forms such, as those presented by statuary marble, PLAN OF INTERNAL BXCAVATION. The survey of tho rock was made by Lieutenant Colonel Wiiliamson, of the Engineer corps United States Army, to whom General Alexandor, of the samo corps, proposed a plan for its removal by blasting in 1968, which embraced the general features of the plan finally adopted and carried oat, This latter the sinking of a shatt through the centre of the rock from « space on its summit, enciosed by a water tight coffer dam, and when this vertical excavation bad reached the required depth below the water level the centre of the rock to be chambered out by excavation until there only remained the thin shell, which retained, of course, the original outward form of the mass until it was finally destroyed by a great explosion of giant powder enclosed tn thirty-eight ale casks and seven old iron tanks, the whole charge representing 43,000 pounds of powder, The work was executed by the en- giteer and contractor, Mr. A. W. Von Schmidt, under the jnepection of Lieutenans W. H, Heuer, of the Corps ot Engineers, who is now a captain and bas becn for a long time in charge of the operations at Hell Gat New York Harbor. The only important change introduced by Mr. Von Schmidt iv carrying out the original plan proposed by General Alexander was the substitution of @ telescope-shaped iron shaft, of which the sections, decreasing in diame- tor with the depth, slid downward, one inside the other, until the roof level gf the internal excavation ‘was reached. DESTRUCTION OF THE BLOBSOM ROCK. When tho great cbarge was fired by means of & galvanic battery placed in g boat about 300 yards from the rock a vastcoluamn of wal about 200 tee in diameter, in which was mingled the débris of t roof rock and pioces of the shoring timbers, wi thrown into the air to ® height of nearly 300 feet, ation of the water, caused by the explo- sion, had subsided, it was found that the Blossom Rock was utterly demolished. The tremendous upheaval of this grent mass of rock by an artiticial volcano created in its centre shows how eflectaally the work was done, and satisfactorily solved an important question regarding the possibility of removing such obstructions when surrounded by deep water. The costof the entire work was $75,000, about the valuo of a single ehip that might have been wreeked on its treacherous ledges, HELL GaTe While the investigations, surveys, plans and prolim- inary works for the removal ot the Blossom Rock were | in progress attention was also directed to the danger- | ous chaune! of Hel) Gate, which presented an effectual barrier to the growth and prosperity of New York in ite vicinity, and particularly to the portion fronting on the Rast River north of that rock-guarded channel. ‘The furious carrents which roll through this. passage | during the ebb and flow of the tides have been fully | described and accounted for tm a recent article pub. lisbed in the Hakan, and it is unnecessary to repeat the description beyond making a general referet.co to its leading points, As stated in the Hrratb article the currents through the Hell Gate passage are croated by a difference in the time and consequently of the level of the tides in New York Bay and Loug Island Sound, The obstructions . . presented by the rocks and narrow channels of the East River to the toflow of the tidal wave creates an accumulation of water in the basin of the Lower Hud- son and New York Harbor, which reaches tbe maximum level fully two hours and a half before the same condi- tion is reached by the tidal wave at Hell Gate. Thus we find that when it is bigh water at Sandy Hook, at say 8:25 P. M., it will be about 9:10 P, M. at Governor's Island and 10:55 P, M. at Hell Gate before the tide reaches its highest lovel. This causes a regular alter. nation of backward and forward flow between the two basins above-named through Hell Gate channel, Tho VARIATION OF THE CURRENT DIKECTIONS, Bavigators have observed, are caused by the conditions Tegniating their flow, such as the tides being spring or neap tides, the direction and strength of the winds favoring « low spring or a high neap tide, the surtacos Presented to the currents by the rocky obstructions and the bydrographical features of the channel. THR RAMOVAL OF THE HELL GATE ONSTRUCTIONS has alwa, sted the attention of our citizens inter at Hell Gate. 2 > Name. e 8 = 3 3 16 5) 14 S| 16 Baldheaded Billy. Blown into Hoyt’s Rock... } deep water Diamond Reet 16(7)} 15.7 Hallett’s Poin No oflect, Total The money expended on these surface blastings was subscribed by citizens’of New York im order to test the Muillefert pian, with the foregoing results. In 1852 Congress appropriated $20,000 for the purpose of re- Section of Hallett’s Point Reef, Showing the Main Shaft, the Galleries and Rock Columns, HIGH WATER LOW WATER Cotfer Dam of Elevation® of Rock Columns Deep and Section of Roof Rock Under Water. Arfangement of Blasting Holes in the Rock Columns and Roof, Wes SNE k ested in the tmprovement of commercial facilities in the vicinity of New York, It has been regarded as one of the most necessary works connected with the har- bor by eminent naval officers who have examined the subject for the purpose of assuring the city against an attack by blockade, and they bave unanimously de- cided that as long as New York possessed only one out- jet for her fleet she was exposod to the danger of being blockaded by powerful hortile squadrons and her com- nvercial interests greatly injured. Surveys were made of Hell Gate in 1848 by Lieutenant Commanders Duvis and Porter, by which a complete knowledge of the bydrog- raphy of the nass was obtained, and in 1851 a system of surface blasting was commenced by M. Maillefert on the following named rocks, which inclade some in the lower East River. The table of operations and results is one prepared by General Jobn H. Newton, of the Corps of Engincers, Uaited States Army, whois now conduct. moving the obstructions and plinced Major Fraser in charge, but the resnits were comparatively insignifi- cant, bocanse the easily removed parts of the rocks bad been aiready blown away, and at the depth at. tained the surface presonted for blasting was greatly increased in area, In 1860 General Newton wok and other apparatus he has succeeded in partly remov- ing the Diamond Reef, near the south entrance to the East River; Coentios Reef, tho Frying Pan Rock, in Hell Gate; the Pot Rock, in the same channel, and Way's Reof, near Hallett’s Point, WALLETT'S POINT REP, The chief danger to tho navigation of the oastern channol of Hell Gate i# presented by the great project ing ledge of stratifiud gneiss roce, known as Hallet’s Point Reof, a section of which, showing its surface prior to and after the great explosion is herewith given, ing the operations for clearing away the obstractions | charge of the operations, and by the ald of aril scows | The danger of this reer is briefly described as follows | by General Newton:-—**Bosides the risk of striking the | reef it produces eddies on*botn sides of it, uecording to the direction of the tidal currents, and is much inthe way of vessels coming down with the ebb in the effort to hug the shore, and thus avoid being thrown on the middle reef, It 1s in the way of small and large vessels equally, and {ts removal, is an essential element in the improvement of tho channel.” THR OPRRATIONS AT HALLETT'S POINT RERF. When it was found by experiment that the pecu- Nar conformation of this great projecting mass of submerged rock rendered any attempt at removing !t by surface blasting fruitless, it was resolved to resort to the more elaborate and tedious plan of drilling adopted by General Newton for the removal ot the otner detached rocks in the Kast River. The surface blasting system was a vory simple one, but not always eftective, Charges of powder weighing about 125 pounds, enclosed tn tin cases made perfectly water tight, wero laid on the surface of the rock and fired by means of a voltaic current, The weight of tho superincumbent water was considered as acting as a sufficient compres- sive force, or tamping, and the effect on the rock in the immediate vicinity of the explosion was to shatter it so that the fragments could be easily actached and re- moved by grappling. The plan answered very well where a sharp projecting rock was surrounded by deep water, into which the débris was blown, but where jarge surfaces presented themselves, such as that of the flallott’s Point Reef, there was no chance for the broken rock to free itself from the main mass, and consequently the plan of surface blasting failed, ‘The system of drilling 1s extremely tedious and ex- pensive, and ag the chief object of the undertaking was to complete tt in the shortest possible time consit= tens with the complete removal of the reef, the late Mr, G. C. Reitheimer’s plan of subaquoous tunnelling for tne removal of rock obstructions in channels was at once adopted by General Newton and indorsed by the other government engineers, This was ‘the first time, so far as known,” according to General Newton, ‘that tunnelling was suggested as a means of removing rocky obstructions in a channel,” and so far as the opera- tions have now progressed at Hallett’s Point tho engineers havo found no reason to regrot the adoption of this mew system, THR CUARAOTER OF THE WORK. ‘The ledge at Hallett’s Point, as shown by the accom- panying plans, projects into the waterway of the East River at Hell Gate in a northeasterly direction, The triangular shaped surface within the line of thirty-two foot soundings extends outward trom its base, rest- ing on the mainland, to iis apex at the thirty-two foot line, about 400 ivet.. The excavation, however, {8 not carried out further than the twenty-six foot line, al- thought at some few points the hoadings have been run the full distance, From the trapezoidal shaped shaft next the shore ten.main headings have been driven, | radiating outward, end these form the basis of tno | general plan ofthe subterranean submarine excava- ton, During the progress of driving these main tunnels supplementary system of excavation was also carried on and the headings were connected by a series of nearly semi-circular galleries, having the centre of the shaft as the centre of gencration of their curvatures, The sectors between the main headings have been again divided by sub-headings until the entire space within the arca desired to be excavated has been hollowed out, the roof or rock forming the present bed of the river being supported ou natural rock columns which have been left untouched for that purpose, As the ledge shelves away into deep water with @ varying slope from the highest point represented by the site of the present main shalt, the length, direction and gradients of the different headings had necessarily to bo subordinated to the peculiar contour of the rocky mass, and the utmosteare had to be observed in preserving the thickness of ten feet between the uppor and lower surfaces of the roof rock whieh covered tho excavation, 1t must be remembered that in exea- vating this immense submarine chamber or system of caverns vast quantities of powerful explosives had to bo employed, and the repeated shocks caused by the rend- ing and tearing away of this solid rock were of course transmitted to every part of its mass in pro- Fortion to their disiance from tho centre of genera- tion. Now, @ carcless use of any of these powerful agents would be likely to shatter the thin shell ot roof rock and cause the drowning out of tho workings by an uncheckable leakage. Ag it was, when tho work of driving the headings was frst started, the survey of the ledge surface w: not complete in the vicinity of the operations, cons: quently the tunnel was excavated at haphazard, and the roof rock between it and the river was thinned away to about four feet thick. The result was a great loakage, which compelled the building up of a masonry shield against the face of the excavation near the roof, and the lowering of the direction of the heading to cor- respond with the surface dip of the ledge into deop water. By tho most careful management and untiring watoh- fulness this vast work is now complete so lar as the excavation goes, and nothing remains but to load all the supporting rock columns, which are already pre- pared and drilled for tho purpose, as described in the Heraxp, and then send the electric spark on itg mission of destruction. HEADINGS AND GALLERIBS. To convey a proper idea of the extent of the opera tions on the Hallett’s Point lege, it is necessary to pre- sent a table giving the lengths of the eral headings and sub-headings with the somi-circular gallerios that connect them, These aggregate over 7,400 feet and in- clude all the cuttings made through the ledge, except that necessary to sink tho main shaft, The débris of this excavation has been brought out of the workings into the main shaft on cars running on narrow | gauge tram roads, the body of the loaded car beiwg | litted from fis truck by a powerful derrick and the con- tents deposited on the “spoil bank” or great heap of finely broken up rock which has been taken out of the shaft since the commencement of the works tn October, 1869. The size of the shaft is 117 feet by 32 feet and ita dopth below the level of low water,-33 fect All the | water that accumulates in the works by leakage is led to the pamps through the headings, so that every part ‘of the excavation is controlled by the pumping power ‘and can be dried without difiloulty by the Cameron and the Blake pumpa in use, TABLA OF LENGTHS OF MEADINGS AND GALLERI Feet, 296.36 135.76 190.98 | Heading No. L . 8 | . 4, main 194.53 | Heading No. 6, main 9 Heading No, 6, main | Heading No, 7, main No. 8, main, Heading No. 9, main, Finding No. 10, main. . Heading No. 2a, intermediate... Heading No, 2b, intermediate, g No. No. No. 2c, intermediate, }, Intermediate, , branch... 2e, intermediate. 2f, intermediate. . . Intermediate, diate. Heading » Heading No, | Heading No, 3a, intermediat Heading No, 5a, intermediate, Heading No, 5b, imtermediate, | Heading No, Se. 3 | Heading No, 6a, Heading No, 6a, branch, Heading No, 6b, Intermedia Heading No, 6e, interm Hoading No. 6d, intermedi Heading No. 6e, intermediat Hending No, 6f, invermeds Heading No. 7a, intermediate Heuding No. 8a, interinediate Heudisg No, 10a, interinediate Heading No. 10b, intermediate... 184.28 Heading No. 100, intermediate 150.65 Heading No. 10d, intermediate 96.67 Heading No. ormediate Heading No. 10f, intermediate. Heading No 10g, intermediate Hieading No. 10k, intermediate, Total Jength of headings... Total length of galerie: Total length of CxCAVations.....ccceceeseees 1,425.67 Tue work on the coffer dam was commenced in July, and on the opening of the main shaft, in October, 1869; and the latter excavation is in size 117 feet by 62 feet, and sank to a depth of 33 feet below mean low water | level . THE GREAT BLAST, “T'll tell you one thing,” said General Newton to a Hanaty reporter at Hell Gate yesterday, ‘all these sightscers who think wo are going to bring heaven and earth together are going to be disappointed. I feol very sorry for those people who are hiring reserved Seats on the Harlem shore at $1 each ‘for this occasion only,’ and Who expect to seo enormous water spouts, upheavals of rocks and all the rest of it, If I could | we know as it is they will oll be disgusved and go away de claring the entire work a big humbug. Why the change in the water level will not be more than from one to two feot atier tho explosion. People in general have an idea that, as we have made a cavern fifteen or twenty feet deep under the bed of the river, the saperincumbent roof of rock, seven to ten feet thick, will fall into the hole and leave that Afteen feet of clear gain in the depth of the river. That is a great mis- take, Tho pillars and root when shattered into pieces will occupy at least twice the space they fill in solid form, so that the real gain in depth of water will be perhaps not more than a foot until alter the broken rock has been dredged up." The work of grappling tor and removing the débris of the reef after the viast will occupy at least one year, even with plenty of tunds, and it seems very doubtful at presont whether money will be forthcoming. Congress appropriated $5,400,000 for harbor improvements the present year and the President signed the bill in due course. Withta a few weeks, however, be has declared that not more than $2,000,000 of the appropriation shall be expended, so that the officials at Hell Gate will get but two-fitths of the amoont they expected. General Newton, when questioned on this subject was very reticent and turned the subject by reverting to the expected ‘show’? on Thursday next, when the mine is tobe fired. When asked if there would not be a very severe earth wave felt along Manhattan Island ho replied ip the negative The shock, he thinks, will not. be felt down town either by concussicn of air or earth wave, Localities along the line of the reef may, he thinks, experience a sligut shock at a distance of half a mile, but i will not be enough to do more than rattie shaky casements. There are now about 39,000 pounds of explosives in the mine, and the entire amount to be used will be between 40,000 and 50,000 pounds. How- ever alarming these figuees may seem when one re- members tho dire effects produced by the explosion of a few ounces of the dreaded compound, the effect will hot be so terrible as would seem on the iirst appear- auce, Many persons expect an earthquake, because they fancy that dynamite exerts all its force downward 1m an explosion, diftering in that respect trom gunpowder, which they’ think “explodes upward.” This is a grea mistake It 18 true that if a small quantity of gunpowder be placed upon a table and touched with @ lighted match it wili burst upward and leave the table unharmed, except, perhaps, that it may be sligutly scorched’ by the heat generated, and that dyna- mite ‘exploded under the same circumstances will go down through the table. Both com- pounds, however, explode spherically—that 1s, with equal force in every direction from the centre; and tho explanation of their different action in the case mentioned is due to the fact that gunpowder can hardiy be said to exploge at all under such circum- stances, so siow is its combustion. It generates gase so slowly that the latier bave time to force aside tha atmospliere, ahd as that offors lees resistance than the suriace of the table all its expansion takes place aud all its force is exerted in that direction, Dywamite, on the other hand, generates gases so fast tbat the alr cannot possibly be crowded out of the way quickly enoughgto make room for them, less resistauce is offered “by the table, and, couscquently, through the table they go. GENERAL NEWTON'S THRORY is that ail the charges in the pillars and roof will have enough to do in shattering the stone by which they are immediately surrounded and that they will produce little or no efiect beyond that. He excepis the charges that aro located at the base of the pillars and which are expected to sever the pillars from the floor, Theso are the ones which will produce whatever slight trembling of the earth may occur when the mine is biown up, and the General thinks that there would be no greatet shock felt if thrice the quantity of explosives were packed in tho stone above tbe points where tho pillars join the floor. the whole, ho 1s afraid that in trying to be cautious and prepare the residents of the reef fur the shock, be has actually made the blowing up appear of much more importance than 1 really is, Many wiseacres of the vicinity, however, shake their heads and geclare that 40,000 pounds o} nitro-glyeerine in comb&istion produces almost enough force to crush acoutinent, “and where,” they ask, “14 that power a goin'?”’ To the depths below the river bed the men are still steadily toting, and had the contractors furnished the material on'time the whole mine would now be charged ready for the primers. Owing to their delay, however, the charging will hardly be completed wo- day. Tho primers, or explodent cartridges, are almost ready for use, and should a fresh supply of dynamite arrive this evening the work of pritming the mine will probably begin.at once and be completed to-morrow; for althougi: the officials are averse to laboring on the Sabbath they will consent to it in view of the fact thas the labor of hundreds of men for five long years, not to mention the mint of money expended, may bo destroyed in the winx of an eye by some accident which would at the same time powder into dust every- body within balf a mile of the piace; when they con- sider that fact they ere anxious to "have the whole business over as soon as possi- ble. When the primers aro ail attached tho cavern will be slowly tlooded by means of a syphon up to the level of the river, Tho syphon is now in posi- tion, and it consists of a heavy iron pipe twelve inches in diamever, A bend at the jower end throws about four feet of it horizontaily along the floor of the shaft, while at the (op an elbow projects horizontally out into the river a snort distance helowthesuriace. The water will be admitted by ng & valve at the top, and flowing throug! the pi ad along the bottom of the headings will rise 80 slow/y as not to displace any of the charges or sweep away the wires. About one day will suffice for the flooding, and the mine will be fired as soon after that event as possible. Every possible precaution has beon taken to guard Against accident at every stage, in case of @ thunder storm arising after (ho primers are in place, and which might perchanve dart along the wires and cause # pre- mature explosion, the ends of each pair of wires will bo joined together to compiete the circuits, and thea all the ends will be thrown into the river, that if the electric fluid should strike any portion of them if wili be dissipated by the water's establishing au equk librium. On the day of the blast—probably on Wednesday ov Thursday next—almost the entire police force of Long Isiand City will be drawn up in @ cordon around th¢ mouth of the shalt, at a little distance. to keep back the crowd, and the river volice of New York will be on hand in their boats, to keep at a distance the hundreds of small boats whose fight seeing occupants weuld permit their curiosity to overcome their discretion, FAST MAIL TRAINS. Tho commission appointed to examine into the oyna. tion of the railway postal service coutinued their invess tigations at the St. James Hotel yesterday morning. Mr. H. J. Jewett, Receiver of the Now York ana Erie Railway Company, was tho first to uppear be- fore the commission. His interview was in reference to the proper basis upon which railroads should be re- munerated tor mail service. In his opinion it should be determinod according to weight, an agreement being had as to the ainount of service, and then a fixed sum agfced upon for a term of, say, four years. Postmaster James iso hud-a hearing before the commission, His conference related almost wholly to the subject of the tast mail service, He gave jan his positive judgment that ninety-nine out of every ono hundred business men of this city anxiously desired a fast mail line. The Postmaster also submitted a re. port upon tho local letter carrier system jor the con- sideration of the members of the commission. Those gentlemen from the Produce Exchange and Chamber of Commerce whose presence had yesterday been expected iniled to put in an appearance, They went not of their iwability to attend, and tt is likely that whatever communication they now have with the commission will be done In writing. On Thursday Jay Gould held a conference with the commiséion, which is stated to have been quite informal and only bad reference to what Mr, Gould in- tends hereafter to propose. This practically closes the session of the commie sion in this city. BROOKLYN BRIDGE, Yestérday tho work of stretching tne first carrier rope into position was continued, under tho supervis. | jon of Mr. Martin, the assistant engineer, and Mr, | Farrington, the master mechanic. The end of the cable was passed over an iron beam six inches in diam eter, on the New York side, and the rope, which, after being towed across the river jay at the bottom of the water at a depth of sixty fect, was gradually tightened by the action of the engine and brought slowly to the surface. It was raised altogether a distance of 251 feet from tho river's bottom to aa altitude of 191 fect above the eur! of the water. The strain on the ime of raising it was equal to nine or ten ton ure. During the time occupied in hoisting th rier’? navigation was, of course, interrupted at that part of the river whieh lics between the piers, but this inverruption did Hot last more than fifteen or twenty minutes, Both sides of the river and adjoining piers ‘were crowded with people. NORTHERN PACIFIC BANKRUPTCY, A motion to discontinue the suit of Mr, E, Sweet against the Northern Pacific Railroad Company, with out costs, was made yesterday, before Justice Pratt, im the Supremo Court, Chambers, of Kings county. Tho motion was made on the gronnd that tho company was insolvent and in a receiver's bands, and that it was useless to sue a corporation that was bankrupt, The plaintif, Who was to bulld the road, taking the est. Mates o] the engineers of the company, found that the work had been largely underestimated, The plamtid claimed that the estimates should have been $100,000 more—$50,000 on the grading and $50,000 on the bridge buildings. Decision was reserved. MOODY AND SANKEY, Mesars. Moody and Sankey, the evangelists, are now at Mr. Moody's home, in Northéeid. They hold ro vival eervices at Brattleboro and Northfield to-morrow (Sunday). Messrs, Moody and Sankey begin their tall and winter work at Chieago October 1. A large bulid- ing, seating 8,000 people, bas been erected in the cen~ tre of tho city for their meetings. Mr. George G. Need ham, the Irish evangelist, accompaniéd by Mr. Steb- give them a little exhibition 1 should like to, for I bing, the singer, of Boston, begins a serics of meetings in the West at the ie tame