504 



experience with moving coil differential galvanometers, for this purpose 

 at any rate is very favourable ^). 



In the manner described we attained a much greater rapidity of 

 measurement than was possible l»y the method described in the 

 previous papers of this sei'ies, and this in its turn increases the accuracy. 



We must also refer to our experience with thermometers in which 

 the wire was sealed to the glass (Comm. N". dob § 1). For tempe- 

 ratures above that of liquid air they are not unsuitable, although 

 even here they are less constant than those with a free thread. 

 After immersion in liquid hydrogen their i-esistance was found to 

 have increased by about one tenth of an Ohm. Each further immers- 

 ion in hydrogen carried with it a permanent change of resistance, 

 so that we replaced these thermometers by other ones with free 

 threads wound on porcelain tubes with a doul)le screw thread baked 

 in. After a thermal treatment, consisting in several immersions in 

 liquid hydrogen followed by moderate heating, these became satis- 

 factorily constant. 



§ 5. Results. In the following table the results of our researches 

 are found. The two first columns contain the hydrogen and helium 

 temperatures calculated from the formula given above. Column 3 

 and 4 contain the corrected temperatures on the absolute scale 

 deduced from the hydrogen and from the helium thermometer, 

 column 5 contains the resistance of the platinum thermometer Ft/. 



The agreement is on the whole very satisfactory. 



We have already mentioned that w^ith thermometers of the kind 

 described an accuracy of about 7,50° i^iight be expected. Our meas- 

 urements show this to be the case; only m a few points larger 

 deviations occur. These can readily be explained by a small defect 

 which will be avoided when we repeat the experiments, namely that 

 the cryostat which had to be used was not quite symmetrically 

 built. When both auxiliary capillaries worked properly this was 

 not of much consequence. But (except fortunately in the determina- 

 tions most important for us viz. at the hydrogen-temperatures) the 

 helium capillary got out of order, so that the distribution of the 

 temperature of the stem of the helium thermometer had to be deduced 

 from the observations with the hydrogen capillary. This circumstance 

 has the greatest influence at temperatures at wdiich the methyl 

 chloride and the oxygen evaporated under reduced pressure, and it 

 is exactly there that the gi-eatest deviations o(!'cur. 



1) Compare Jaeger, Zeitschr. f. Itistrumentenkunde 1904. 



