( 78 ) 



annexed plate shows such a cryostat in a vacuum glass of much 

 larger dimensions (9 cm. internal diameter) which during some 

 years has satisfied high requirements. 



The apparatus has served for measurements ^) with a differential 

 thermometer of which one reservoir was tilled with hydrogen the 

 other w^ith nitrogen, for a comparison of a thermoelement with the 

 hydrogen thermometer (cf. Comm. N". 89) and for measurements 

 on the isothermais of diatomic gases (cf. Comm. N". 69, April '01 

 and N". 98, April '02). If the plate is compared with Comm. N". 83 

 no much further explanation is wanted. The same letters designate the 

 same parts. The connections of the cryostat with the regulating apparatus 

 for constant temperature are the same as on Pis. I, V and VI of Comm. 

 N". 83. The stirring-apparatus to obtain a ?i«zy<9>'»i temperature is moved 

 by an electromotor as is the case with the cryostat represented there. 

 During the measurements with the differential thermometer the tempera- 

 ture was regulated according to the indications of a thermoelement 

 (which is described in detail in Comm. N°. 89 published lately). 

 In the comparison of the thermoelement O with the hydrogen thermo- 

 meter one of the thermometerreservoirs on the annexed plate was 

 replaced by a resistance thermometer (double cylinder according to 

 Comm. N". 93, PI. I, fig. 2, with improvements which will be described 

 later on). Moreover in the measurements of isothermais the piezometer 

 (cf. Comm. N". 69, PI. I) w^as put in the place of the second 

 thermometerreservoir. 



In order to secure a symmetrical distribution of the current in 

 the bath mica screens, (wdiich also serve for insulation) are used if 

 necessary (for instance in the resistance thermometer), and a tube 

 similar to the thermoelement O was mounted symmetrically with 

 the latter. 



The agreement between the mean temperatures of the measuring 

 apparatus and the temperature indicator is further promoted by 

 making the mean height of the two equal. 



As with the cryostats of Comm. N". 83 we can reach by means 

 of this one a constancy to within 0.01° C. For everything relating 

 to this I refer to Comm. N". 83. 



A silvered vacuumglass being used, there was arranged a float 

 (not to be seen in the figure) to show the position of the level of 

 the liquid. 



The stopper and the w^ay in which the thermoelement is fixed 



1) The completion of the calculations of these measurements, on the subject of 

 which we shall soon publish a communication, requires some new determinations 

 and the application of some corrections, 



