

Intelligence and Miscellaneous Articles. 385 



Nevertheless in these conditions the mercurial column rises with 

 starts which cause considerable errors. They are completely de- 

 stroyed by giving a rotatory motion to the pistons, which is easily 

 obtained. 



I have hitherto investigated only the compressibility of water 

 and that of ordinary ether. The piece in which the piezometer is 

 compressed is a steel cylinder 1-20 metre in height ; it is hooped 

 for its entire length except part of the breech ; its internal dia- 

 meter is 3 centim., and its sides are 8 centim. in thickness. It was 

 cast and hooped at the cannon foundry of Firminy. This cylinder 

 is fixed vertically in a large copper reservoir, so that it can be 

 worked with in melting ice, or in a current of water at a constant 

 temperature. 



The reading of the volumes of the compressed liquid was made 

 by the following method, which was pointed out to me by Prof. 

 Tait. A series of platinum wires are soldered in the stem of the 

 piezometer, as in fire-alarm thermometers ; these wires are con- 

 nected by a metal spiral with a resistance of two ohms between each 

 wire, and the prolongation of which passes through the short 

 cylinder by means of a special insulated joint. The current of a 

 battery reaches the mercury in which the stem is immersed through 

 the steel cylinder. It will thus be seen how galvanometric indica- 

 tions may give the precise moment at which the mercury rising in 

 the stem, owing to the compression of the liquid, successively 

 reaches each platinum wire. 



The liquid of the piezometer and the liquid which transmits the 

 pressure in which it is immersed become considerably heated by the 

 pressure; this makes the experiments very long; a considerable 

 time is required to counterbalance the mass, which is a bad con- 

 ductor ; the readings must be repeated until the indications of the 

 manometer are constant in contact. The series of observations 

 made with decreasing pressures produce the same effect in the oppo- 

 site direction ; the mean of the results is taken, and their general 

 agreement shows that the whole method leaves really little to be 

 desired. 



,We see by this what gross errors may have been committed with 

 the other devices hitherto used for measuring volumes in analogous 

 conditions. 



Ether and water have been studied at zero and at two adjacent 

 temperatures, the one of 20° and the other of 40°. 



For both liquids the direction of the variation of the coefficient 

 of contractibility with the temperature is the same under very 

 strong pressures as under very weak. Water continues to form an 

 exception; its compressibility diminishes as the temperature in- 

 creases, in the above limits ; the variation seems, however, to 

 diminish at the highest pressures. 



The coefficient of the variation with the pressure, as was easily 

 to be foreseen, gradually diminishes as the pressure increases ; and 

 this is the case throughout the entire scale of pressures, contrary 



Phil. Mag. B. 5. Vol. 22, No. 137, Oct 1886. 2 D 



