( 2()i ) 



A more detailed investigation of these questions ought to be made 

 of course witii more accurate means. It lies at hand to use the 

 method of Fizp]au. Many years ago one of us (K. 0.), during a 

 visit at Jena, discussed with Prof. Pulfrich the possibility of placing 

 a dilatometer of Abbe into the Leiden cryostat, but the means 

 of procuring the apparatus are lacking as yet. Meanwhile the 

 investigation following this method has been taken in hand at the 

 Reichsanstalt ^). A cryostat like the Leiden one, which allows of 

 keeping a temperature constant to 0,01" for a considerable time, 

 would probably prove a very suitable apparatus for this investigation. 



Travers, Senter and Jaquerod^) give for the coefficient of expan- 

 sion of a Jiot further determined kind of glass between O'' and — 190° 

 the value 0,0000218, From the mean coefficient of expansion from 

 0^ to 100° we conclude that this glass probably is identical with 

 our Thüringer glass. 



The mean coefficient of expansion between 0° and — 190° for 

 Thüringer glass found at Leiden in 1903 is 0,00002074. 



§ 2. Measurement of the coefficient of expansion of Jena glass and 

 of platinum between (f and — 182''. 



The rod of Jena glass used was the same as that of Comm. N°. 85. 



At the extremities of the platinum tube of 85 cm. length glass ends 

 were soldered of the same kind as the Jena rod. For the determina- 

 tion of the mean temperature of the ends thin platinum wire was 

 wound round these extremities which wire at either end passed over 

 into two platinum conducting wires and was enveloped in layers 

 of paper in order to diminish as much as possible the exterior 

 conduction of heat. '» 



The temperature of the middle portion of the Jena rod was also 

 determined by means of a platinum wire wound round it as in 

 Comm. N°. 85. The rod was further enveloped in thin paper 

 pasted together with fishglue, and to test the insulation the resistance 

 was measured on purpose before and after the pasting. The tempera- 

 ture of the bath was determined halfway the height of the bath 

 by means of the thermo-element constantin-steel (comp. Comm. N°. 95^, 

 this meeting). 



This temperature was adopted as the mean temperature of 

 the platinum tube, which was entirely surrounded with the liquid 

 gas and was only at its extremities in contact with the much less 



1) Henning, afterwards Scheel, Zcilschr. f. Instrk. April 1905, p. 104 and April 1906, 

 p. 118. Randall, Phys. Revie v 20, p. 10, 1905 has construcLed a shnilar apparatus. 

 3) Travers, Senter and Jaquerod, Phil. Trans, A 200. 



