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Proceedings of the British Association. 



phenomenon of elliptical polarization ; and he showed that this at- 

 tempt had failed. M. Laurent supposes the particles of the lumini- 

 ferous ether Hot to be simply material points, but to have dimensions 

 which are not insensible when compared with their distances ; and on 

 this hypothesis he deduces a system of differential equations, the in- 

 tegrals of which he conceives to represent the phenomenon in ques- 

 tion. The integral given by M. Laurent is, however, absurd, though 

 this circumstance was not noticed by M. Cauchy, in the remarks and 

 comments which he made on M. Laurent's memoir. The true inte- 

 gral of these equations (supposing them to be correctly deduced) was 

 shown by Prof. M'Cullagh to indicate motions of the ether which do 

 not correspond to the observed phenomena. 



Mr. E. Hodgkinson gave an account of some further experiments 

 " On the defect of Elasticity of Rigid Bodies". These experiments 

 originated in the suggestion that possibly some of the results which 

 Mr. Hodgkinson had communicated at Cork (see Athen. No. 827), 

 had originated in the friction caused by the supports of the extremities 

 of the bars on which the experiments were perfomed. He had there- 

 fore, in these later experiments, placed strong friction wheels as sup- 

 ports for the ends of the bars ; he had also changed the mode of 

 measuring the deflection. He had previously used a wedge graduat- 

 ed on the side ; he substituted for this a fine screw with a divided 

 micrometer head, by which he could measure the 10,000th part of 

 an inch of a deflection. He then gave the numerical details of the 

 sets taken by various bars after they have been loaded and then re- 

 lieved. The most striking general results were, that the index of 

 the power of the load to which he found the set taken most nearly 

 proportional was 2 ; that every load, however trivial, caused a set, and 

 that this set did not entirely disappear when the bar was given time 

 to recover its state, but in general diminished greatly. 



Dr. Scoresby inquired if Mr. Hodgkinson had tried whether a 

 vibratory motion excited among the particles of the bar would enable 

 them to recover their original arrangement. Mr. Hodgkinson had 

 not, but promised to attend to the hint. Dr. Robinson suggested 

 that the vibratory motions should not be excited with violence suffici- 

 ent to cause mechanical derangement of the particles. Lord Rosse 

 stated two facts bearing on Mr. Hodgkinson's investigations ; one, 



