l86 • French National LiJIifute. 



comparinc; it cither with the. fun's limb, or to a very confidera- 

 ble fpot which appeared on that body, and of which the dia- 

 meter was 25' of a degree. PTe determines the mon)ent of 

 the esrefs of Mercury's centre at 7' 6" true time; and this 

 plaueVs paffagc of the meridian 55'^ before that of the fun's 

 centre. 



C. Meffier's memoir contains a detailed view of the deter- 

 minations he obtained, and is accompanied with a drawing 

 which reprefonts the apparent route of Mercury on the fun. 

 It exhibits a kimlnous ring, with which Mercury feems to 

 be furrounded. This circumftance, pecuUar to the obierva- 

 tif>n of C. Meffier, was remarked by him in the tranfit of 

 1799; it was obferved alfo at Montpellier, in 1736, bv Plan- 

 tade; and at Upfal, in 1736, by M. Profperin. This ring 

 exhibited a very faint light, and of a colour different from 

 that of the fun. Its diameter towards the end of the tranfit 

 ■was 1' J 9'', and that of Mercury 17". 



EXPERIMENTAL PHILOSOPHY. 



On the Method of mngiietiz'mg to Suluration. 



To apply with conflancy to the fame objefts, and to vary 

 their combinations in every manner pollible, are the condi- 

 tions on which nature confents to difclofe her fecrets to thofe 

 who intcrrotrate her. It was by fulfilling them with aruaffi- 

 duity and facracltv worthy of fuccefs that C. Coulomb attained 

 to his Interelling difcoveries in eledlricity and magnetlfm, and 

 bv Impofing on himfelf the tafk of Uluftratlng every part of 

 thefe important branches of phllofophy. Mngnet'izing, the 

 perfeftlng of which is of fo much importance to navi- 

 gators, could not efcape his attention. \'ery v.igue notions 

 had hitherto been acquired in regard to the intenfity of the 

 majinetic force which fteel is capable of acquiring in its dif- 

 ferent ftatcs ; and it was meafured in general by the weight 

 of the piece magnetized. But it is of the greateft import- 

 ance here to know the energy w'ith which needles tend to 

 return to their direftion after they have been removed from 

 if and this C. Coulomb meafures dircftly, by defermin- 

 inc, according to Borda's views, and by means of very nice 

 fufpenfion, how niany ofcillations thefe needles perform in a 

 given time. 



After comparins; the methods of magnetizing prnpofed 

 by Duhamel, Knight, and yEpinus, to give a needle all the 

 direii'^ing force it is capable of receiving, the author decides 

 in favour of that of /Eplnus. He found that it is moft ad- 

 vanta<Teous to make the needles long and broad, but not 



thick. 



