GO ANNUAL OF SCIENTIFIC DISCOVERY. 



tube, in turn duly joined to the barometric cistern. Let the boat or vessel be 

 propelled on a course. The air-vessel will be dragged along the bottom, and 

 as the water must have free access to the bag enclosing the air, its pressure 

 will compress the air to a density due to the depth. This pressure will be 

 communicated along the tube to the vessel or boat, and being received on 

 the mercurial surface, Avill raise a column to such a height that its weight will 

 equal the weight of an equal column of the water, whose height is the depth 

 to which the air-vessel is sunk, or rather that of the lowest part on which the 

 pressure acts. As this depth varies, the height of the column will also vary. 

 The relation of these heights is expressed by the specific gravity of mercury 

 divided by the specific gravity of the particular sea or other water of which the 

 soundings are being made. It would be necessary to make occasional obser- 

 vations with the hydrometer, and in the case of tidal streams these should be 

 quite frequent." The detailed construction of such an apparatus is given by 

 Lieut. Hunt, in Silliinan's Journal, No. 76, July, 18-53. 



GAS-LIGHTS ON RAILROAD CARS. 



The following plan for lighting cars with gas has been adopted with great 

 success on the New Jersey railroad. Each car is provided with a wrought- 

 iron cylinder, of a capacity of four and a half cubic feet. The cylinder is 

 of a strength capable of sustaining 500 pounds pressure. The heads, for 

 greater security, are made concave. The gas is compressed under a pressure 

 of twenty atmospheres (300 pounds to the square inch), 90 cubic feet of gas 

 being forced into each cylinder. Each car is provided with a cylinder, which 

 is placed upon a shelf under the car floor, and coupled in the usual manner 

 with a pipe leading to the burner within. An improved regulating contri- 

 vance controls the delivery of the gas to the burner under all pressures, and 

 is interposed between the cylinder and burners, so that the light is always 

 steady. The pressure of the gas ensures the continuity of light, no matter 

 what the concussions or roughness of the road. 



The method of charging the cylinders with gas, adopted on the New Jersey 

 road, is simple and expeditious. Near the Company's machine shop, at 

 Jersey City, a stack of the cylinders are arranged, into which the gas is forced 

 by the rapid movements of a steam-pump, to a pressure of about 450 pounds. 

 The cylinders are connected together by small pipes, and thus form a strong 

 and capacious reservoir. A conducting-pipe leads from the stack to the large 

 depot on the Hudson river, where all the passenger cars arrive and depart, a 

 distance of a quarter of a mile. The conductor terminates in a horizontal 

 pipe running beneath the depot platforms, with stop-cock openings at suita- 

 ble intervals. When the car cylinders are to be charged, an attendant 

 simply couples them to the conducting-pipe, and opens a stop-cock. The 

 gas then instantly rushes into the cylinders and fills them, under the pressure 

 of the reservoir, and they are read} 7 for use. The filling of the cylinders for 

 a whole train occupies only a few minutes, and the work of supplying all the 

 trains with gas is, we are told, easily performed, from beginning to end, by 

 one man. Scientific American. 



TUNNEL UNDER THE ALPS. 



It is generally known that the immense work of boring a tunnel under the 

 Alps, between Modane arid Bardoueche, had commenced ; but we have now 



