340 RECORD OF SCIENCE FOR 1886. 



the time of exposure. These Hues are obliq-ie, their direction being 

 made up of two rectangular motious, that of the plate and that of the 

 bubble. The v^elocity of motion of the plate is fixed by the vibrations 

 of a tuning-fork, and the exact direction of its motion by a dotted 

 line. Knowing the angle which one of the slantiug lines in the photo- 

 graph makes, the velocity of the bubble, and so that of the jet, may be 

 readily deduced. (C. R., Januarj^, 1S8G, cir, 1G5; Phil. Mag., March, 

 1886, V, XXI, 285.) 



Subsequently Vautier employed a rotating mirror for the same pur- 

 pose. The jet as before flows vertically downward and its image is 

 thrown on the screen by means of a lens ; between the lens aud the 

 screen is placed a plane mirror movable about a vertical axis. As the 

 bubbles fall vertically, the moving mirror causes a horizontal displace- 

 ment in its image ; so that upon the screen an inclined line is seen, the 

 resultant of the two rectangular component velocities. The tangent of 

 the inclination angle is the ratio of these velocities. His results con- 

 firm Torricelli's law to within one eightieth part — (C. 11., August, 1888, 

 cm, 372.) 



Amagat has adopted the principle of the differential manometer for 

 measuring very high pressures, the necessary conditions being that the 

 pistons be completely mobile aud at the same time perfectly tight. The 

 large piston rests on a cushion of castor-oil which transmits the press- 

 ure to the mercury. The small piston which receives all the pressure 

 at the top becomes quite tight if after being soaked in oil and put in 

 its place it is wetted on its base with a sufiQciently viscous liquid, such 

 as molasses, which answers i)erfectly. Under these conditions, the pis- 

 tons even being somewhat free, there is no real leak but only an ex- 

 tremely slow oozing which does not affect the measurements even up to 

 pressures above 3,000 atmospheres. The water was compressed in a 

 steel cylinder 1.2 meter long, hooped for its entire length except a part 

 of the breech. Its diameter was 3 centimeters and its sides were 8 cen- 

 timeters thick. The reading of the volumes of the compressed liquid 

 was effected by means of i)latinum wires fused into the stem of the 

 piezometer, by means of which the current from a battery reaches the 

 mercury in the steel cylinder. The precise moments at which the mer- 

 cury rising in the stem reaches the platinum wires successively, as the 

 liquid suffers compression, are thus noted on the galvanometer. The 

 following are the coefficients of compressibility for water at 17.0° and 

 for ether at 17.4° : For water between 1 and 262 atmospheres, 0.00()0i29 ; 

 between 1,331 and 1,781 atmospheres, 0.0000302 ; and between 2,5'JO and 

 2,981 atmospheres, 0.0000238 ; at 3,000 atmospheres therefore the volume 

 of water is diminished by one-tenth aud its compressibility coefficient 

 by one-half. For ether between 1 and 151 atmospheres, 0.00015G; 870 

 and 1,213 atmospheres, 0.000003; aud between 1,023 aud 2,002 atmos- 

 pheres, 0.000045. (0. 11., August, 1886. cin, 429 ; Phil. Mag., October, 

 1886, V, XXII, 384.) 



