200 Prof. Silas W. Holman on the Effect of 



of the plan impossible for one whose available time has been 

 fully occupied with laboratory instruction. It will be seen 

 that the last of the observations given were made in April 

 1880. Since that date it has been wholly inconsistent with 

 the author's duties and health to continue the work ; and the 

 incomplete results are now presented in the hope that, despite 

 their limited range, they may be a contribution of some per- 

 manent value to the subject treated. 



The expenses of the investigation have been mainly defrayed 

 by an appropriation granted by the American Academy of 

 Arts and Sciences from the Rumford Fund for researches on 

 Light and Heat. 



The objects of the investigation were concisely stated in the 

 paper of 1876. The extension of the work was looked to for 

 the development of data, which not only should furnish another 

 experimental check on the deductions of the kinetic theory of 

 gases, but should provide material of sufficient precision (ap- 

 proximating to that with which the coefficient of expansion 

 of gases is known) to serve as a part of that experimental 

 basis on which the complete theory of gases, and indeed of 

 molecular physics in general, must eventually rest. The cri- 

 tical review of the method, given at p. 204, is intended to 

 furnish the material for the formation of a judgment as to 

 how far this object has been fulfilled in the case of the gases 

 investigated. 



Apparatus. 



The apparatus used is shown in the schematic section given 

 by the accompanying diagram. It is in principle the same 

 as that used in the former measurements. The dried gas is 

 transpired successively through two glass capillaries of about 

 30 centim. in length, from a space containing the gas at a 

 measured pressure to another space from which the gas is 

 continuously exhausted as fast as it enters, and which is thus 

 maintained at a constant and measured pressure. The pres- 

 sure of the gas in the intermediate space is also measured. 

 The capillaries are maintained at known or measured constant 

 temperatures, A B being usually packed in finely pounded 

 ice, and D C being in a jacketed double oil-bath, of which the 

 temperature is maintained nearly constant by regulating the 

 flame of the gas-burners, and is measured by the thermometer 

 with its bulb at D, the entrance to the capillary. Both inner 

 and outer oil-baths are continuously stirred by an agitator 

 moved to and fro through the troughs by a water motor with 

 connections, not shown in the sketch. This arrangement 

 maintained temperatures as high as 225° constant, within 



