OF ARTS AND SCIENCES. 



75 



Investigations on Lioht am> Heat, made and published wholly or in part with 

 appropriation from the Ruhford Fund. 



V. 



ON THE MECHANICAL EQUIVALENT OF HEAT, WITH SUB- 

 SIDIARY RESEARCHES ON THE VARIATION OF THE 

 MERCURIAL FROM THE AIR THERMOMETER, AND ON 

 THE VARIATION OF THE SPECIFIC HEAT OF WATER. 



By Henry A. Rowland,* 



wi the Johns Hopkins University. 

 Presented June 11th, 1879. 



CONTENTS. 



I. Introductory Remarks 

 II. Thermometry .... 

 (a.) General View of Thermome- 

 try 



(6.) The Mercurial Thermometer 



(c.) Relation of the Mercurial and 



Air Thermometers . . 



1. General ami Historical 



Remarks . 



2. Description of Apparatus 



3. Results of Comparison . 

 (d.) Reduction to the Absolute 



Scale .... 112 

 Appendix to Thermometry . . 116 



III. Calorimetry 119 



(a.) Specific Heat of Water . . 119 

 (o.) Heat Capacity of the Calo- 

 rimeter .... 131 



78 



s3 



B3 



97 



IV. Determination of Equivalent 



. 137 



(a.) Historical Remarks . . 137 



1. General Review of Meth- 



ods .... 137 



2. Results of Best Deter- 



minations . . . 140 

 (6.) Description of A pparatus . 155 



1. Preliminary Remarks . 155 



2. General Description . 157 



3. Details . . . .158 

 (c.) Theory of the Experiment . 183 



1. Estimation of "Work done 163 



2. Radiation . . . .168 



3. Corrections to Thermom- 



eters, etc. . . . 171 

 (rf.) Results 173 



1. Constant Data . . 173 



2. Experimental Data and 



Tables of Results . . 174 

 Concluding Remarks, and Criticism 

 of Results and Methods . . 197 



I. — INTRODUCTORY REMARKS. 



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

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

 is used almost daily by the physicist. Yet, when we come to consider 



* 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 Ameri- 

 can Academy of Arts and Sciences at Boston, from the fund which was insti- 

 tuted 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 investigation. 



