196 



that the magnetism of the needle is the result of the difference of two 

 actions, it may be further inferred, that the diffusion of motion in this 

 case is almost comparable with that of a spark from a flint and steel 

 in the case of light. 



The author next alludes to a proposition which he advanced in the 

 second number of his Contributions, namely, that the phenomena of 

 dynamic induction may be referred to the known electrical laws, as 

 given by the common theories of electricity ; and he gives a number 

 of experiments to illustrate the connection between statical and dyna- 

 mical induction. 



The last part of the series of experiments relates to induced cur- 

 rents from atmospheric electricity. By a very simple arrangement, 

 needles are strongly magnetized in the author's study, even when the 

 flash is at the distance of seven or eight miles, and when the thunder 

 is scarcely audible. On this principle, he proposes a simple self- 

 registering electrometer, connected with an elevated exploring rod. 



Dr. Hare made an oral communication, in continuation of his 

 remarks, made at the last meeting, on platinum and the metals 

 accompanying its native grains. 



He stated that, agreeably to trials made by Mr. J. R. Eckfeldt, of 

 the mint, and Mr. Boye, both possessing balances of exquisite accu- 

 racy, and being eminently skilful in the use of them, the specific gra- 

 vity of a fused globule of iridium of sixty-seven grains in weight, ob- 

 tained from a warranted specimen of iridium, purchased of Johnson 

 and Cocke, of London, was inferred to be 21.80. Agreeably to this 

 result, and likewise the previous observations of Breithaupt upon cer- 

 tain specimens of native iridium, this metal, either in this state, or as 

 obtained in purity by chemical skill and consolidated by fusion, must 

 be allowed that pre-eminence in density over all other bodies, which, 

 until of late, was conceded to platinum. In fact, as contrasted with 

 platinum, obtained by fusion without subsequent hammering, the dif- 

 ference would be more than one-tenth. Specimens of hammered pla- 

 tinum which weighed 21.23, on fusion were reduced to 19.70. 



An important inference from these results was, that, as iridium is 

 the only impurity in standard platinum, a high specific gravity indi- 

 cates neither a superior degree of purity nor malleability. A piece of 

 standard malleable platinum, of a very fine white colour, presented to 

 Dr. Hare by his excellency Count Cancrine, the Russian minister of 

 finance, as of the best quality of Russian platinum, proved, according 

 to Eckfeldt, to have a specific gravity of 21.31; when a specimen, 



