( 200 ) 



Thence follows 



Jena glass 16"« a — 781 b = 90 



ki = 2343 k, = 272. 



Thüringer glass (n". 50) a = 920 b = 120 



k, = 2761 k,= 362. 



1903. 



Secondly it remained uncertain whether the mean temperatures 

 of the ends were exactly identical with those found after the method 

 laid down in § 4 of that Comm. The execution of the control- 

 determination as described in Comm. N°. 85 § 4 (comp. § 4 of this paper) 

 proved that in this respect the method left nothing to be desired. 



Moreover, availing ourselves of the experience acquired at former 

 determinations, we have once more measured the expansion .of the 

 same rod of Jena glass and have reached about the same results 

 which, owing to the greater care bestowed on them, are even more 

 reliable. 



Lastly it was of importance to decide whether the great increase 

 of h at low temperatures also occurred with other solid substances 

 and might therefore be considered as a property of the solid state 

 of several amorphous substances. Therefore and because it was 

 desirable also for other reasons to know the expansion of platinum 

 we have measured the expansion of a platinum rod in the same 

 way as that of the glass rod. Also with platinum we have found 

 the same strong increase of h, when this is calculated for tlie same 

 interval at lower temperatures, so that cubic equations for the lengths 

 of both substances must be used when we want to represent the 

 expansion as far as — 182°. 



After these measurements were finished ScheeTj (Zeitschr. f. Instr. 

 April 1906 p. 119) published his resuU that the expansion of pla- 

 tinum from — 190° to 0° is smaller than follows from the quadratic 

 formula for the expansion above 100'^. For the expansion from -{- 16° 

 to — 190^ Scheel finds — 1641 u per meter, while — 1687 f* would 

 follow from our measurements. But he thinks that with a small 

 modification in the coefficients of the quadratic formula his observa- 

 tions can be made to harmonize with those above 100^. Our result, 

 however, points evidently at a larger vahie of b below 0*^. 



The necessity of adopting a cubic formula with a negative coeffi- 

 cient of f may be considered as being in harmony with the 

 negative expansion of amorphous quartz found by Scheel (1. c.) 

 between — 190° and 16° when we consider the values of a and h 

 in a quadratic formula for the expansion of this substance between 

 0" and + 250°. 



