1896.] 



Scientific Instruments used by Joule. 



345 



X. " Keport of the Examination of some of the Scientific 

 Instruments employed by the late Dr. Joule." By J. D. 

 Chorlton, B.Sc., Joule Scholar. Communicated by Pro- 

 fessor Arthur Schuster, F.R.S. Received March 17, 1896. 



Having been appointed by the Royal Society to the Joule Scholar- 

 ship, and entrusted with the examination of some of the instruments 

 employed by Joule in his. scientific work, I called upon his son, 

 Mr. B. A. Joule, in whose possession were such of the instruments as 

 had not already been presented to the South Kensington Museum or 

 other places. Mr. Joule very kindly placed the instruments at my 

 disposal, and I am much indebted to him for the trouble he took in 

 search ing his house for anything that might have been laid by. 



Most of the instruments I removed to the Physical Laboratory at 

 Owens College, where there were greater facilities for examining 

 them. Throughout the research I have been greatly aided by the two 

 volumes issued by the Physical Society of London, in which all 

 Joule's scientific papers are collected, and in every case I have 

 referred to the pages in these volumes where a complete description 

 of the instrument under examination may be found, with accompany- 

 ing diagrams. 



The following list comprises all the more important instruments 

 remaining at Sale : — 



Two electric current meters. 



The last apparatus for determining the mechanical equivalent of 

 heat. 



An electromagnetic engine. 

 A new balance. 

 A mercurial air exhauster. 

 A new form of dip circle. 

 Two air pumps. 



Several thermometers and an instrument for calibrating thermo- 

 meters. 

 Two tangent galvanometers. 



All of these instruments were either made by Joule himself or 

 from his design and under his directions. 



Two Electric Current Meters ('Collected Papers,' vol. 1. pp. 584—589, 



also p. 542). 



As a good deal of discussion has lately been carried on about the 

 difference in the value of J obtained by different methods, it seemed 

 important to find the value in our present units of the constant of the 



