NATURAL PHILOSOPHY. 165 



tent action of the piston in the pump causes, of necessity, more or 

 less shock with every movement, which rapidly wears out the 

 apparatus, and renders it unserviceable. These French instru- 

 ments dispense entirely with the pump, and use instead the dis- 

 placing action of a solid plug or piston or some equivalent body, 

 forced by a screw or other mechanism against or into the liquid 

 (oil) with which the barrel of the press is charged. Thus, by the 

 continuous action of a screw in one of these new presses, forcing 

 a solid piston along a narrow tube connecting with the barrel, a 

 steady and perfectly manageable pressure of great intensity is 

 obtained. 



He also described another instrument, in which the action is 

 produced by means of a small catgut string, wound up by an out- 

 side winch acting on a reel within the cylinder ; two cylinders 

 may be used, so that, when the pressure is exerted in the one 

 containing the wound coil of catgut, the other, which contains 

 the unwound coil, is receiving, by a valvular arrangement at the 

 bottom, the fluid necessary for the compressive action, when its 

 turn comes to receive the additional substance of the wound coil. 

 By this alternate winding and unwinding of a simple catgut coil, 

 in two cylinders which communicate by separate tubes with the 

 barrel of the pump, a pressure of any desirable amount can be 

 slowly and steadily attained, as for testing the strength of bars 

 of steel, etc. 



^CONDUCTION OF SOUND BY HYDROGEN AND AIR. 



Prof. Tyndall, on a lecture on *' Vibratory Motion," delivered at 

 the Royal Institution, showed a novel experiment, illustrating the 

 very low conductivity which hydrogen possesses for sonorous 

 vibrations. A bell, struck by clock-work, was placed under the 

 receiver of an air-pump, and the air exhausted as perfectly as 

 possible. It was stated that by applying the ear close to the glass 

 a faint sound could still be heard. The exhausted receiver was 

 then filled with hydrogen, when the bell was again heard to 

 sound, although faintly. On pumping out the hydrogen all trace 

 of sound entirely disappeared, even though the ear were placed 

 close to the receiver. Hydrogen being about 15 times lighter , 

 than air, it might be considered that sound would travel in an 

 atmosphere of hydrogen as readily as it would in air exhausted to 

 2 inches barometric pressure. But on trying the experiment it 

 was found that when 2 inches of air were passed into the receiver, 

 it allowed far more sound of the bell to pass through it than did 

 the full atmosphere of hydrogen, showing that conductivity for 

 sound depended upon something more than mere density. It 

 was then shown that sound travelled with almost the same ease 

 through air exhausted to half its normal density that it did at the 

 ordinary pressure. Cliem. News. 



ON PERFECT HARMONY. 



Mr. H. W. Poole, in the " American Journal of Science," for 

 July, 1867, has written an interesting and elaborate article, sup- 



