.VERIFICATION OF EQUIVALENT. 163 



Note, 1 891 : — " I have never had occasion to regret my advice, 

 Dr. Mann soon obtained my brother's confidence, and 

 proved a most attentive and judicious friend as well as 

 medical adviser. I think I may fairly say that I had the 

 privilege of saving my brother's life for a quarter of a 

 century. 



In August and September, 1873, Joule spent six weeks 



with his family at Douglas ; in 1874 he occupied himself in 



making slight improvements in the mercurial displacement 



pump, which he had invented before his health gave way, 



and in 1875, he read a short paper " On a Glue Battery." 



It was about this time that he resumed his work on the 

 " Verification of the Mechanical Equivalent of Heat," com- 

 menced for the British Association. But owing to un- 

 fortunate investments, his income having become much 

 diminished, he found himself unable to undertake the very 

 considerable expense the investigation involved over and 

 above the small grant originally made by the Association. 

 This becoming known, the Royal Society made him a 

 grant of £200 out of the fund of £4,000 placed at their 

 disposal by the Government. With this assistance, Joule 

 during the years 1876 — 7 perfected the apparatus and made 

 the experiments, devoting himself entirely to the work. 

 The results were published in a paper "New Determination 

 of the Mechanical Equivalent of Heat," which was read 

 January 24th, 1878, and printed in the Phil. Trans., 1878^ 

 Part II. 



In these experiments the old thermometers were again 

 used. Before using them, however, the values of the 

 graduations were again determined with the utmost care, 

 and with every precaution experience could suggest, the 

 result being that although the freezing point had risen 



