( :j9i) ) 



quartz tube, nitrogen was gradually admitted. The meniscus began 

 then to become gradually fainter. The incandescenl lamps placed 

 behind the slil made the inner wall <>f the quartz tube look like a 

 streak of light, in which the meniscus made a notch. By moving 

 the eye to and fro in froni of ihis notch I could ascertain the 

 presence of the liquid mirror as long as possible. The temperature 

 al which the meniscus disappeared, was noted down; also the tem- 

 perature al which the liquid mirror returned on decrease of pressure 

 in die vapour-jacket. 



First the 7V of the mixture # = 0,1 was determined; compared 

 with Cailletet and Colardeau's observations this <j;ive a decreaseoi 

 tt J in the critical temperature. So there was no doubt but a minimum 

 of temperature was present in the plaitpoint-line. 



To see whether the decrease would continue, ,r = 0,2 was deter- 

 mined; we found ±364°; the 7'/.. though rising, was still below the 

 value given by Cailletet and Colardeau for. <• = (). In order to 

 determine the place of the minimum more accurately, the first component 

 [x = Oj and the mixture # = 0,06 were then examined; finally also 

 #=0,5 and #=0,35 with a view to the course of' the plaitpoint 

 line beyond the minimum. 



The observations have been put together in the subjoined table; 

 they have been reduced on a thermometer tested at the Reichsanstalt, 

 which does not show any deviation at 300 \ but points one degree 

 too low al 400°. 



The meniscus 

 disappeared at 



The meniscus 

 returned at 



The meniscus The meniscus 



disappeared for the returned 



second time at again at 



Graphically represented we obtain the following 7#-projection of 

 the plaitpoint line: 



