TRANSACTIONS OF THE SECTIONS. 



355 



has already observed that this is not the case. When the large 

 cyHnder is filled with water, the bottle is to be immersed in it. 

 If the tube a « is full of water, a little of it must be expelled, 

 which can be done by heating it gently with the hand, or better, 

 by introducing a wire into it. As the bottle may be considered 

 as a water thermometer, it is easy to ascertain whether it is in 

 thermical equilibrium with the water in the cylinder. The air 

 in the tube c d must likewise be brought to the same tempera- 

 ture with the water, before it is ultimately immersed. When 

 the pumping cylinder shall be placed in its box, the piston 

 must be at G H. If the large cylinder is full of water, part of 

 it will be expelled through the siphon t u s. Now the piston is 

 to be lifted up by means of the screw, whereby the pumping 

 cylinder is filled with w^ater. When this is done, the siphon is 

 taken away, and the tube r * is stopped by a screw appertaining 

 to it. The experiment is most conveniently performed by three 

 persons ; one turning the screw, the second observing the height 

 of the water in the tube a a, and the third observing the volume 

 of the air in the tube c d : the last writes down the numbers ob- 

 served. Now, the point where the water stands in the tube of 

 the bottle is to be noted. The descending piston having re- 

 duced the volume of the air in the tube c d to the point desired, 

 the observer of it takes hold of the handle of the screw, and 

 keeps the volume unchanged until the other observer has settled 

 the point to which the water is brought down, and writes down 

 the observation. When the piston is lifted up to its first place, 

 the screw at r is to be opened, and the state of the water in the 

 capillary tube again noted down. I commonly make ten or more 

 such observations, one after another, which is performed in less 

 than ten minutes when the operators are accustomed to work to- 

 gether. An example will illustrate the use of the observations. 



2 A 2 



