xu 



change was in great measure clue to his unflagging advocacy of an 

 improved system. 



It is, however, in Mr. Christie's labours as one of our more distinguished 

 Fellows that the Society is principally interested. Our Transactions are 

 enriched with a number of papers from his hand, and he took an important 

 share in promoting the great advance in both theoretical and experimental 

 knowledge of magnetical science, which received its impulse from the obser- 

 vations made during the Arctic voyages in 1818 and 1819. The leading 

 idea which runs through Mr. Christie's theoretical discussions of his 

 various experimental results, he first stated as an hypothetical law in a 

 paper published in the Cambridge Philosophical Transactions for 1820. 

 In a paper read before the Royal Society in June 1824, he gave an ac- 

 count of some of his experiments for the determination of the effects 

 of temperature upon magnetic forces, and established a correction for 

 temperature in the experimental determination of the magnetic inten- 

 sity, which had been previously overlooked. Mr. Christie was the first 

 to observe the effect of the slow rotation of iron in producing magnetic 

 polarity, and, at his suggestion, the very interesting series of experiments 

 which he originated, and which are given in detail in a paper pubhshed 

 in the Philosophical Transactions for 1825, were repeated by Lieutenant 

 Foster, R.N., during the expedition to the north-west coast of America in 

 1824, under Captain Parry, with results even more striking than his own, 

 owing to the diminished horizontal component of the magnetic force. 



In 1833 a paper by Mr. Christie upon the magneto-electric conduction 

 of various metals was selected by the Council of the Royal Society as the 

 Bakerian Lecture for the year. In this paper he shows, both experimentally 

 and theoretically, that the conducting power of the several metals varies 

 inversely as the length, and directly as the square of the diameter of the 

 conducting wire, thus obeying the same law as that previously discovered 

 by Sir Humphry Davy and Professor Cumming, in the cases of voltaic and 

 thermo-electricity ; although his conclusion as to a difference in the order 

 of their conducting powers could not now be maintained His impor- 

 tant remark in this paper — that magneto-electricity cannot be developed 

 at the same instant in every part of a system, and that the action 

 on the remote parts of the wire cannot be absolutely simultaneous with 

 that on the parts in the immediate neighbourhood of the magnet — 

 appears to have been almost prophetic, now that we are able to submit 

 this vast velocity to a definite measurement, by timing the transmission of 

 effect through a journey of three thousand miles. 



The effect of the solarrays upon the magnetic needle very early engaged Mr. 

 Christie's attention, and he showed, by a series of experiments detailed in 

 papers published in the Philosophical Transactions for 1826 and 1828, that 

 the direct effect of the solar rays is definite and not due to any mere calorific in- 

 fluence. He then also threw out the suggestion that terrestrial magnetism is 



