88 M. Achille Cazin on Internal TVorJc in Gases, 



is maintained in a horizontal position by an iron support F, fixed 

 to a table on which all the apparatus stands. The stopcock is 

 turned by means of a lever, G G. 



In order to introduce the gas into the reservoirs, a vacuum is 

 created by using the tubulure H, for instance ; the gas is then 

 allowed to enter, being dried in its passage; and this double 

 operation is repeated a second time, as usual. 



The small tube I connects the reservoir A with the open-air 

 manometer K K. The height of the mercury in this manometer 

 is read by the aid of a copper scale 4 metres in height, divided 

 into millimetres, fixed vertically along the open branch of the 

 manometer, and provided with two verniers. 



The small tube L connects the reservoir B with the open-air 

 manometer M M ; the difference of the levels is measured by a 

 cathetometer. 



To the tubes I K, L M, are connected, by means of three-way 

 tubes, tubes NO, P 0, which terminate in a gas-pump. This 

 pump serves to pass a portion of the gas from reservoir B to re- 

 servoir A. 



The manometer which is intended to follow the change of 

 pressure of the gas daring the expansion, consists of a glass tube 

 of-two vertical branches, Q Q ; one of these has a cylindrical en- 

 largement, within which the interior level of the liquid always 

 remains ; the displacements of the exterior level are noted along 

 a vertical scale. The liquid varies with the nature of the gas. 

 The communication of this manometer with the reservoirs is 

 by means of the small reservoir R, which is firmly fixed on the 

 table; it consists of a small copper cylinder divided into two 

 compartments, and contains a conical valve the rod of which 

 passes through a stuffing-box (fig. 3). The upper compartment 

 communicates with the tube S of the reservoir B (fig. 2), and 

 the lower compartment with the manometer Q. The valve is 

 closed by the pressure of a spring; and in order to open it con- 

 siderable pressure must be exerted on the rod. This valve must 

 be opened at a certain moment after the opening of the stop- 

 cock C. For this purpose the axis of the stopcock is provided 

 with a kind of cam, which just presses on the rod of the valve 

 K when the stopcock C is quite open. The manometer Q can 

 thus be connected with the reservoir B at any time by turning 

 more or less quickly the large stopcock. 



We have now to describe the apparatus which measures the 

 time. 



A strip of paper (fig. 2) is unrolled from the roller a and 

 rolled on the roller b by the descent of a weight. The motion 

 is rendered nearly uniform by the small vanes d. The strip of 

 paper is guided by two little rollers, e } /. A pencil, g> rests on 



