(508 ) 



they remain elastic enough to permit the movements of the cord. 

 A regular up and down molion of the stirhng apparatus is secured 

 by the wheel X;- 



§ 5. A constant temperature is attained by continually adjusting 

 the pressure, at which the liquid in tlio hath evaporates, to the 

 indications of a resistance thermonuHer // |)iaced concentrically in the 

 bath. A sensitive thermometer forms an iidiereiit |)arl of llie cryostat 

 under consideration when it is lo he used lor \(m-v coiistaut tem|)e- 

 ratures and the dimensions allowing a resistance thermometer to be 

 ijilroduced, tlie hittei- has been chosen as the most trustworthy. Tts 

 inner diameter controls the greatest cross section ol the measnring 

 apparatus which can be immersed in the bath, and therefore, as 

 in our case, it must correspond to that of the tid)e F^. The con- 

 struction of this thermometer has Ikhmi described in detail by H. Meit-ink 

 (Comm. 77 Febr. '02) with a view to a com[)arison between it and 

 the hydrogen thermometer referred to above. The leads pass through 

 the openings /{•,„, A'^„ of the ebonite rings /?, and R^, and then 

 through the stopper into the tube 1\^. On the [)lates I and II they 

 are indicated by the same letters as on the plate of Comm. 77. 



When the bath has reached the re(piired temperature the galvano- 

 meter in the Whkatstonk's bridge, which serves to measure the 

 resistance of ^^ is adjusted to zero by introducing suitable resistances. 

 As soon as the deviations of the galvanometer make it necessary, a 

 sign is given to the assistant, charged with the regulation of the pressure 

 in (he cryostat, who then raises or dinunishes the }«-essure, whereby 

 the temi)eratnre in the bath rises or fixlls. 'V\w great volume of the 

 cryostat is iiere very useful in ciiecking oscillaliojis in pi-essin-e. The 

 arrangements required for the regnhilion of pi-essnre are shown in plate 

 1, the separate [)ieces of ap[)aratus to scale and tiic connections schema- 

 tically. (Conq). Comm. 51 Sept. T)9, pi. IV). The assistant uses 

 the oil manometer A',, which is connected to the cryostat l)y X^ 

 and A', (comp. pi. II Comm. 51) and the cock X^^, the cock 

 A\, being oi>en. If we shut the cock X^^ the motion of {\\q oil 

 enables us to very accurately watch the variations of the pressure 

 in the cryostat by means of the dilTerencc between the pressure 

 in it and f>f the quantity of gas temporarily shut off in the reserAf)ir 

 .V„. If through some cause or other the variations of pressure 

 increase considerably, or if we want to stop the regulation, or to 

 proceed to another [)ressure, the oil is prevented from running over 

 by our opening tlie cock A',,. The pressure in the cryostat is varied by 

 more or less opening tiie line cocks V^^ and V^., of the regulation 



