16 



ON THE MECHANICAL EQUIVALENT OF HEAT, WITH SUB- 

 SIDIAEY RESEAKCHES ON THE VARIATION OF THE 

 MERCURIAL FROM THE AIR THERMOMETER, AND ON 

 THE VARIATION OF THE SPECIFIC HEAT OF WATER l 



[Proceedings of the American Academy of Arts and Sciences, XV, 75-200, 1880] 



INVESTIGATIONS ON LIGHT AND HEAT, made and published wholly or in part with 

 appropriation from the RUMFOBD FUND 



Presented June llth, 1879 



CONTENTS 



I. Introductory remarks .... 343 



II. Thermometry 345 



(a.) General view of Thermom- 

 etry 345 



(&.) The Mercurial Thermometer 346 

 (c.) Relation of the Mercurial 



and Air Thermometers 352 



1. General and Historical 



Remarks .... 352 



2. Description of Appa- 



ratus 358 



3. Results of Comparison 366 

 (d.) Reduction to the Absolute 



Scale 381 



Appendix to Thermometry . 384 



III. Calorimetry 387 



(a.) Specific Heat of Water . 387 

 (6.) Heat Capacity of the Calo- 

 rimeter 399 



IV. Determination of Equivalent . 404 



V. 



(a.) Historical Remarks . . . 404 



1. General Review of 



Methods 405 



2. Results of Best Deter- 



minations .... 409 

 (&.) Description of Apparatus 422 



1. Preliminary Remarks . 422 



2. General Description . 424 



3. Details 426 



(c) Theory of the Experiment 430 



1. Estimation of Work 



Done 430 



2. Radiation 435 



3. Corrections to Ther- 



mometers, etc. . . 439 

 (d.) Results 441 



1. Constant Data . . . 441 



2. Experimental Data and 



Tables of Results . 441 

 Concluding Remarks and Criti- 

 cism of Results and Methods 465 



I. INTRODUCTOKY REMARKS 



Among the more important constants of nature, the ratio of the 

 heat unit to the unit of mechanical work stands forth prominent, and 



1 This research was originally to have been performed in connection with Professor 

 Pickering, but the plan was frustrated by the great distance between our residences. 

 An appropriation for this experiment was made by the American Academy of Arts 

 and Sciences at Boston, from the fund which was instituted by Count Rumford, and 

 liberal aid was also given by the Trustees of the Johns Hopkins University, who are 

 desirous, as far as they can, to promote original scientific investigations. 



