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by some of our best mathematicians. The objection 

 advanced to it by Professor Thomson, of Glasgow, that 

 the one was, to a certain extent, a constrained, and the 

 other a perfectly free motion, was certainly a valid objec- 

 tion ; but there were some difficulties attending the sub- 

 ject which required to be removed by further experiment. 

 He (Professor Elliot) had shown the greater part of these 

 experiments to the Liverpool Polytechnic Society in the 

 year 1839. Since that time the subject of rotatory 

 motion had become a fashionable study among mathema- 

 ticians, having been taken up successively by Professors 

 Magnus, Wheatsone, Powell, Foucault, Smyth, and 

 Maxwell. Foucault's experiment for shewing the sta- 

 bility (perfect or partial) of a rotating disc during the 

 earth's rotation was not new in theory, as it had been 

 described more than twenty years before by Mr. Sang ; 

 nor was it in his (Professor Elliot's) opinion practically 

 successful in shewing the earth's rotation, since its suc- 

 cess depended altogether upon the adjustment of the 

 apparatus, and the only mode, he believed, of making 

 that very delicate adjustment, was by trying if it pro- 

 duced the very motion it was intended to demonstrate. 

 It could be made to shew the rotation of the earth, or 

 not to sheAv it, just as it was balanced. Professor 

 Smyth's apparatus he had previously described. Pro- 

 fessor Maxwell, of Aberdeen, was the last who had pro- 

 duced any thing new on the subject of rotatory motion, 

 and in a set of beautiful experiments, and some refined 

 calculations, he had advanced further into the subject 

 than any of his predecessors. Professor Maxwell's prin- 

 cipal object was to throw light on the theory of Saturn's 

 ring. In his essay, for which he lately had the high honour 

 of gaining the Adams' Prize offered by St. John's College, 

 Cambridge for the best dissertation on that subject, 

 Professor Maxwell objected to the applicability of his 



