DISPLAY OF CHARACTER. 159 



formance of the Electro-Magnetic Engine," the Society was 

 also indebted to a paper communicated to the Society (not 

 by a member), criticising the conclusions Joule had arrived at 

 in 1845 as to the economic limits of electro-magnetic engines ; 

 and although this critical paper was written in ignorance 

 of the subject, the Society owes thanks to the author for 

 having drawn from Joule a dissertation on his earlier work, 

 which, to those who heard it, was a revelation as to what 

 Joule must have been in his earlier days. Joule himself 

 enjoyed the opportunity, and insisted that the paper should 

 be read and the author of the paper should be invited to 

 attend. As may be supposed, there was a strong feeling of 

 indignation amongst the members at the apparent insolence 

 of the attempt, but the discussion was confined to the 

 author and Joule, who not only answered the objections, 

 but, in the most dignified and courteous manner, explained 

 to the author the elementary mistakes he had made, dis- 

 playing the clearness of his memory as to the details of this 

 complicated research made a quarter of a century before. 



Besides the papers already mentioned, Joule made ten 

 other short communications to the Society between 1869 

 and 1872. Three of these were on his Dip Circle, in which 

 the dip needle was suspended from a balance by spider lines, 

 and the seven others were severally on ; — Physical Properties 

 of Bees' Wax; — Photographs of the Sun; — Sunset at 

 Southport; — the Magnetic Storm of Februarys 1872; — the 

 Polarization of Platina Plates by Frictional Electricity; — the 

 Prevalence of Hydrophobia ; — and a Mercurial Air Pump ; 

 this was the first of the now common displacement pumps. 



In addition to the work which these entailed, Joule was 

 at this time engaged preparing his new apparatus for what 

 was to be his last determination of the mechanical equi- 



