260 



Professor Dewar 



[Jan. 16, 



The lamp was placed inside this vessel, the wires connecting it with 

 the machine being brought through the bottom of the stand. A tube 

 passed through the porcelain base, which allowed a current of dry air 

 to be forced through the vessel. A small aperture in the top of the 

 tin vessel allowed the glass tube coming from the positive pole to pass 

 with little friction, through which the products from the arc were 

 drawn. This annular vessel was very convenient, not only for exa- 

 mining the products formed in the arc, but also those formed outside 

 of it, and the water flowing round it served the double purpose of 

 keeping it cool and enabling a determination of the amount of total 

 radiation in heat units to be made. 



Fig. 2. 



Vessels containing pumice moistened with sulphuric acid and 

 phosphoric anhydride were placed inside the cylinder in order to dry 

 the interior as completely as possible. 



Numerous experiments made by forcing perfectly dry air into the 

 vessel through the tube A, and drawing it out by the tube B through 

 a weighed sulphuric acid bulb, gave after an hour a few milligrams 

 of increase, owing, no doubt, to some slight defect in the soldering of 



