48 Dr. J. A. Harker on 



tion difficult to attain if any third bearing be placed on 

 the shaft. In a calorimeter as described, holding 5 litres, 

 whose stirrer rotates at about 300 a minute, the level of 

 the water on one side remains permanently about one 

 centimetre higher than at the other, and any small objects 

 in the water can be seen to make the circuit from top to 

 bottom of the calorimeter many times in a minute. 



After many failures, an apparatus was at length con- 

 structed in which the steam entered at the side as in 

 Regnault's form, and in which only such steam as was 

 condensed within the calorimeter itself could possibly 

 reach the condenser. This is shown in Fig. 3. Since 

 a calorimeter of this form required a special ther- 

 mostat to hold it, I first endeavoured to find, whether 

 a double layer of the lead-tube jacket previously described 

 would protect any reasonable length of tubing through 

 which steam was passing from appreciable cooling, and 

 finding it to be satisfactory, decided to bring the steam 

 tube through a slot in the side of the thermostat. This 

 thermostat was a double-walled vessel of stout zinc, 

 holding about 50 litres, the interior being of such a size 

 that, the calorimeter being supported in it by cork feet, 

 a space of 5 cm. was left around it on every side. The 

 inner wall, lid, and bottom of the thermostat were covered 

 with platinised copper sheet, which was capable of taking 

 a high polish, and did not tarnish with the rapidity of 

 a silvered surface. The detail of the leading-in tube is 

 shown in Fig 3. The steam from the boiler passes along 

 the jacketed tube A B, which is screwed into the ebonite 

 tube C D. This is cemented tight, and held by screws 

 in a brass collar, which is bevelled so that it is inclined 

 to the vertical at about 45 , and is soldered to a stout 

 brass plate, let into the flat side of the calorimeter. To the 

 condenser tube is fastened a similar brass plate, through 

 which are soldered steel screws projecting outwards. The 



