Some Experiments on the Latent Heat of Steam. 47 



in a position about half-way between the centre and 

 circumference, leaving but little room for any large object 

 in the water. I found, however, that by making the 

 calorimeter oval in section and by placing the rotating 

 stirrer, having two or three sets of screw blades, near one 

 end, arranging the direction of its rotation that the water 

 was lifted, excellent stirring could be obtained. At the 

 same time a large amount of space in the calorimeter was 

 left free for the condenser, and the thermometer need not 

 be exposed to any danger from being caught by the fast- 

 moving blades. In cases where the space over the 

 calorimeter was not fully taken up, I found it extremely 

 convenient to fasten the brass stirrer shaft direct to the 

 armature of a small Cuttriss motor supported by a steel 

 rod, with universal joint, from a firm iron retort stand. 

 The motor can be driven by one or two small accumulators, 

 and its direction of rotation changed or speed altered 

 simply by rocking the brushes. This arrangement saves 

 all troubles with belts or gearing. Conduction of heat 

 along the stirrer shaft is prevented by a piece of ebonite, 

 into which the brass wire carrying the blades and the steel 

 spindle of the motor are screwed. When it was incon- 

 venient to have the motor so close to the calorimeter, a 

 framework of iron was clamped at a considerable height 

 to a heavy iron retort stand, carrying a rotating shaft 

 which could be driven from the motor by a cord and 

 suitable pulleys. This shaft was adjusted to be perfectly 

 vertical, and the stirrer was hung freely from it, being only 

 loosely screwed to it by one or two turns of thread, several 

 rubber washers being placed between the two parts. A 

 cup placed on the shaft prevented the oil from the two 

 bearings above from reaching the calorimeter. With this 

 kind of stirrer, when all is in good adjustment, the lower 

 part, when rotating in the water, steadies itself, and no 

 vibration is perceptible even at very high speeds, a condi- 



