ENGINEERING. 



311 



under a pressure of five atmospheres through 

 flexible tubes. On the Swiss side the new 

 Brandt perforator was employed. This ma- 

 chine excelled the performance of the Ferroux 

 apparatus need at the other end, which is the 

 latest improvement in the percussion perfo- 

 rator. The new perforator consists of six or 

 eight veritable drills, with a diameter of 70 

 millimetres, which bore into the rock with a 

 rotarv movement under a hydraulic pressure 

 of from 60 to 100 atmospheres. The differ- 

 ence in the speed at which the work proceeded 

 in the different Alpine tunnels shows the prog- 

 ress made in boring machinery. The Mont 

 Oenis tunnel advanced at the rate of 3,637 feet 

 a year ; the St. Gothard at the rate of 5,474 

 feet ; and the Arlberg at the rate of 7,080 feet. 

 The improvements reduce the expense in a 

 still greater ratio, the Arlberg tunnel having 

 cost only $750 per lineal metre, as compared 

 with $1,250 per metre in the St. Gothard, and 

 $2,000 in the Mont Oenis works ; although a 

 part of this saving was due to the relative 

 shortness of the Arlberg bore. 



The work of carrying away the excavated 

 material in mountain tunneling is as difficult, 

 and consumes quite as much time, as that of 

 excavating. The gases from the explosives 

 render this task unwholesome and sometimes 

 dangerous. In the Arlberg the miners escaped 

 ill effects by covering their mouths and nos- 

 trils with sponges steeped in vinegar. 



At first, owing to the hardness of the rocks 

 on the western side, and to the inflow of enor- 

 mous quantities of water, the stipulated rate of 

 progress, about ten feet a day, could not be 

 made; but after the water was subdued the 

 advance was more rapid than the prescribed 

 speed. The gallery was driven on a level with 

 the bottom of the tunnel, and not, as formerly, 

 on the Belgian system, i. e., on a level with 

 the top. The cost of the tunnel itself is esti- 

 mated at 18,-000,000 florins, including the pre- 

 miums earned by the contractors for early com- 

 pletion, in which premiums they allowed their 

 workmen to share. The cost of the whole line 

 will be about 40,000,000 florins. 



Mersey Railway Tunnel. The headings of the 

 tunnel under the river Mersey met in the cen- 

 ter before the end of tb.3 year. Though insig- 

 nificant in length, the river being less than a 

 mile broad at that point, this tunnel is a work 

 of great difficulty, owing to the low level at 

 which it has to be carried under the deep 

 waters of the Mersey, the toughness of the new 

 red sandstone, the amount of pumping neces- 

 sary to remove the immense quantity of water 

 which perforates through this porous rock, the 

 work of lining the gallery to stop this inflow,, 

 and the precautions which were necessary 

 against a possible fault in the geological forma- 

 tion and the inrush of water from the river. 

 Fortunately, the stratum was found to he con- 

 tinuous. The roof of the tunnel is separated 

 from the bed of the river by a thickness of 30 

 feet. The length of the tunnel is 1,753 yards. 



The seven-foot heading was excavated partly 

 with Col. Beaumont's boring-machine, which 

 was set for inch per revolution, equal to f 

 inch per minute, which was a slower speed 

 than was made in the gray chalk of the Chan- 

 nel tunnel. Through this seven-foot drift- 

 way the water which entered flowed down the 

 incline to the shaft at each end and was got 

 rid of by means of the steam-pumps. The 

 tunnel was excavated at a higher level, the 

 work proceeding at some distance in the rear 

 of the advance of the drift-way. The tunnel is 

 semicircular, and has a breadth of 26 feet and 

 a height of 20 feet above the rails, the radius 

 of the curve varying from 40 feet at the base 

 to -i 3 feet in the arch. The gallery, as it was 

 quarried out, was lined all round with massive 

 walls of brick and cement. The heavy blocks 

 of stone, which were blasted out with gelatine, 

 were removed on cars in a constant rotation. 

 On the Cheshire side, where the Beaumont 

 borer was used, a compressed-air locomotive 

 of Col. Beaumont's invention was employed to 

 remove the excavated rock. 



Hitherto the only connection between Liver- 

 pool and Birkenhead, where the railroads of 

 Cheshire and Wales converge, has been by 

 ferry. Various plans for carrying a railroad 

 across the Mersey, by a high bridge or a tun- 

 nel, have been proposed by engineers before. 

 The tunnel finally constructed is the shortest 

 and most direct route, one end emerging in the 

 center of Liverpool, and the other in the cen- 

 ter of Birkenhead. The grades are conse- 

 quently heavy. The tunnel is expected to be 

 opened to traffic in 1885. 



East River Bridge. The suspension-bridge 

 over the strait called the East river, which 

 separates New York from Brooklyn, on Long 

 Island, was completed and formally opened on 

 May 24th. The project of a bridge to connect 

 the two cities and furnish safe and rapid com- 

 munication, was originally brought forward by 

 William C. Kingsley, President of the Bridge 

 Trustees, and Henry C. Murphy, his prede- 

 cessor in office. Mr. Kingsley selected the 

 site, and had plans and estimates prepared, as 

 early as 1865. The Bridge Company was or- 

 ganized in 1867, with a nominal capital of $5,- 

 000,000, the amount of the preliminary rough 

 estimate of the engineer, $500,000 of which 

 was subscribed by citizens who formed the 

 company, $3,000,000 was to be furnished by 

 Brooklyn and $1,500,000 by the city of New 

 York. In 1875 the bridge was made a State 

 work, and placed in charge of a board of trus- 

 tees. John A . Roebling, the originator of wire 

 suspension-bridges, was the engineer. His 

 estimates in 1867 made the cost of the bridge 

 $7,000,000, and of the approaches $3,800,000. 

 The estimated time of construction was five 

 years. A commission of bridge engineers ap- 

 proved his plans. Congress passed an act in 

 1869 authorizing the construction, and in June 

 of that year the Secretary of War decided 

 that it would not impede navigation, .providing 



