804 Mr. F. B. Young on the 



about 0*1 of a calorie was absorbed at the upper meniscus 

 and evolved at the lower ; the dissipation of heat from the 

 bell, moreover, occurred through two thicknesses of glass 

 separated by a thin film of liquid. 



The tests have only a rough quantitative value since the 

 tubes were not identical in their dimensions. They suffice to 

 show, however, that (a) the ether should be prepared shortly 

 before being placed in the tubes ; (b) the last traces of 

 gaseous impurity can be removed only with the utmost diffi- 

 culty ; (c) if the tubes are to be sealed with the blowpipe 

 the pressure of the ether vapour should previously be reduced 

 to a minimum. Each of the above experiments was checked 

 by duplicate tubes. 



In Table I. are included for reference the proportions 

 of the tubes filled by the liquid at 0° C. and the critical 

 temperature of the ether in tubes VII., XIII., and XIV. 

 (Tube XII. exploded before observations could be made.) 



The temperature given is that at which the meniscus was 

 first perceived as the ether was very slowly cooled. Since 

 in neither of the tubes was the mean density exactly equal 

 to the critical density, the actual Cagniard-Latour tempe- 

 rature (<9 C ) is probably slightly higher than that given. The 

 critical temperature "for tube XIV. is the mean of seven 

 observations, and the critical temperatures for tubes VII. 

 and XIII. are obtained by direct comparison with tube XIV., 

 the tubes being observed simultaneously. 



B. Disposition of Apparatus. 

 The tube under observation was supported on a glass rod 

 in the vapour jacket E (fig. 4). This jacket was surrounded 

 by two guard-tubes forming a double air jacket, whilst an 

 inner tube F, which was widened at the bottom to fit the 

 vapour jacket rather closely, still further protected the tube 

 from temperature disturbances. A coil of metal tube H acted 

 as a condenser, a stream of cold water being passed through 

 it. The tin cone K deflected any drops of condensed liquid 

 to the sides of the vapour jacket. The asbestos cone G 

 protected the vapour from the heat of the flame which 

 was placed beneath. The vapour jacket was placed 

 between the poles L of a powerful electromagnet which 

 was mounted on a small counterpoised lift so that it could 

 be readily raised or lowered. By means of the magnet 

 the bell C (fig. 2) could be raised at will. The upper portion 

 of the experimental tube was in some cases surrounded by an 

 open coil of fine iron wire N having a resistance of about 

 2 ohms, the ends of which were connected through the needles 

 M to electrical terminals. The vapour jacket was connected, 



