WARDLE ROAD, SALE. 1 65 



similar to that used by Hirn, who has laboured so earnestly 

 and successfully on this subject He has described it as 

 follows " — with an extract of Hirn's paper. 



In this research Joule made five series of experiments at 

 ■different speeds, each series involving from 6 to 21 separate 

 determinations. The agreement between the results so 

 obtained was very close, and on carefully reducing these to a 

 mean, the result arrived at was 772*55, which differed from his 

 final determination in 1849, 772*692, by less than two inches 

 of fall, or one part in five thousand, thus verifying his final 

 result ^^2 to within a thousandth part, and establishing it 

 as being, as yet, the most accurate, as it is the most difficult, 

 of all the accurate and difficult determinations which have 

 gone to define the dynamical theory of matter. Con- 

 sidering that the powers of observation and contrivance 

 required to obtain this accuracy are such that none of the 

 many eminent experimental physicists who have worked 

 since 1850 have rivalled Joule in his work, the repetition 

 of his experiment of 1849 in 1878, after an interval of 29 

 years, and at the age of sixty, is an unprecedented per- 

 formance, and shows, more emphatically than was other- 

 wise possible, the special powers as an experimentalist 

 with which he was endowed, and of which advancing years 

 had, as yet, in no way deprived him. 



This was the last experimental research of any 

 magnitude that Joule undertook. In 1877, he again 

 changed his residence ; having purchased No. 12, Wardle 

 Road, Sale, he removed into it, and resided there till 

 his death, using an out-building and the cellars of his 

 house for the purposes of keeping his apparatus and making 

 experiments. He paid two visits this year to Mr. Binney, at 

 Douglas, and was there again in 1879. 



