MOTIVE POWER OF HEAT. 93 



same quantity of heat; which leads to the assertion 

 that steam, compressed or expanded mechanically 

 without loss of heat, will always be found in a 

 saturated state if it was so produced in the first 

 place. The vapor of water so made may then be 

 regarded as a permanent gas, and should observe 

 all the laws of one. Consequently the formula 



A + B log v 

 ~ A' + B' log v 



should be applicable to it, and be found to accord 

 with the table of tensions derived from the direct 

 experiments of M. Dalton. 



We may be assured, in fact, that our formula, 

 with a convenient determination of arbitrary con- 

 stants, represents very closely the results of experi- 

 ment. The slight irregularities which we find 

 therein do not exceed what we might reasonably 

 attribute to errors of observation.* 



We will return, however, to our principal sub- 

 ject, from which we have wandered too far the 

 motive power of heat. 



We have shown that the quantity of motive 

 power developed by the transfer of caloric from 

 one body to another depends essentially upon the 

 temperature of the two bodies, but we have not 



* Note D, Appendix B. 



