46 



PROCEEDINGS OP THE AMERICAN ACADEMY 



theory, as well as from its prominent plaee among the phenomena of 

 gases, renders it very desirable that we should know the true law. 



In endeavoring to arrange some new form of apparatus for a more 

 accurate study of this law, the idea of a differential arrangement 

 was sugjrested to me by Professor Pickering. This has been the 

 origin of the following method. Two glass capillaries, AB and 

 CD, were placed side by side, each in a tin trough to contain a bath 

 to regulate the temperature of the gas. Air-tight glass and rubber 

 connectors extended from G to the gauge F, and to tlie end D of one 

 capillary. The ends ^ and Cof the capillaries were connected with 

 the gauge E by means of a T joint of glass. Tiie end A of the second 

 tube communicated with the external air throusfh the chloride of 

 calcium tubes -^aad I. The size of the connectors at the ends of AB 



Fig:. 2. 



and CD was sufficient to allow the gas to assume the temperature of 

 the bath. The tube at G was connected with a large flask, from which 

 the air was continuously exhausted by means of a Richards' jet aspira- 

 tor. The size of this flask rendered the pressure co:istant in spite of 

 slight variations in water pressure. An inspection of this arrangement 

 will show that when the flask is exhausted, and a vacuum produced at 

 G, the air will enter at A under the atmospheric pressure, and will 

 pass with constantly diminishing pressure to G ; so that, at any inter- 

 mediate point, as the junction of the two tubes at BC, we shall have a 

 pressure intermediate between the two extremes. It will also be seea 

 that the same volume of air is successively transpired through ^5 and 

 CD; providing that there be no leak, which was carefully guarded 

 against by making all the joints about C, B, and B — which were the 

 only ones that affected the results — as tight as possible. By the two 

 baths we may have the gas transpired successively through AB and 



