648 



SCIENCE. 



[N. S. Vol. XI. No. 278. 



spiral tube joins the inner and outer test- 

 tubes of which B is made, thereby making 

 an opening into the interior at C. The re- 

 sistance thermometer D and leads E pass 

 through a rubber cork, F, and the exhaus- 

 tion takes place through C. In this way the 

 cold vapors are drawn over the outside of 

 the hydrogen vacuum vessel, and this helps 

 to isolate the liquid from the convective 

 currents of gas. To effect proper isolation, 

 the whole apparatus ought to be immersed 

 in liquid air under exhaustion. Arrange- 

 ments of this kind add to the complication, 



reducing the pressure, the resistance di- 

 minished to 0.114 ohm, and kept steady 

 for some time. The lowest reading of re- 

 sistance was 0.112 ohm. This value cor- 

 responds to —2.391° C, or only one degree 

 lower on its own scale, than the boiling 

 point at atmospheric pressure, whereas the 

 temperature ought to have been reduced at 

 least 5°, under the assumed exhaustion, 

 according to the gas thermometer scale. 

 The position of the observation on the 

 curve of the relation of temperature and 

 resistance for N^o. 7 thermometer is shown 



Temperature in decrees Centigrade. 



so in the first instance the liquid was used 

 as described. The liquid hydrogen evap- 

 orated quietly and steadily under a dimin- 

 ished pressure of about 25 mm. N'aturally 

 the liquid does not last long, so the resist- 

 ance has to be taken quickly. Just before 

 the reduction of pressure began, the resist- 

 ance of the thermometer was 0.131 ohm. 

 This result compares favorably with the 

 former observation on the boiling point, 

 which gave a resistance of 0.129 ohm. On 



on the accompanying diagram (Fig. 3). 

 As a matter of fact, however, this platinum 

 thermometer was, when placed in liquid 

 hj^drogen, cooled at starting below its own 

 temperature of perfect conductivity, so that 

 no exhaustion was needed to bring it to 

 this point. The question arises then as to 

 what is the explanation of this result ? Has 

 the platinum resistance thermometer ar- 

 rived at a limiting resistance about the 

 boiling point of hydrogen, so that at a lower 



