Royal Society. 215 



The lamp being then removed to the iron leg, the needle 

 receded 2° before the heat had attained redness. Thus the 

 conducting power of iron suffered more from heat than that 

 of copper. 



18. Iron being thus proved to be inferior in conducting power, 

 both for heat and electricity, in circumstances directly in point, 

 to copper, cannot owe its thermo-electric superiority to that 

 property; and, extending the analogy to other metals, the in- 

 ference at the beginning of this section would seem to be re- 

 futed. But the following section will bring the question be- 

 fore us in a different point of view. 



[To be continued.] 



XL I. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



April 15. A PAPER was read, entitled, "On Improvements in the 

 <£*- Instruments and Methods employed in determining 

 the Direction and Intensity of Terrestrial Magnetism." By Samuel 

 Hunter Christie, Esq. M.A'F.R.S. 



The tedious nature of the observations by which the direction and 

 intensity of the terrestrial magnetic force are determined, and the un- 

 certainty attending the results when obtained, have long been a sub- 

 ject of regret to all who are engaged in the investigation of the phe- 

 nomena of terrestrial magnetism. Sensible of this, the author's at- 

 tention has at different times been turned to the improvement of the 

 instruments employed for these purposes ; and in this communication 

 he proposes methods by which he considers that these instruments 

 might be so improved that the results should be obtained with greater 

 facility and also with greater certainty. The uncertainty attending 

 the results obtained with the dipping needle, as at present construct- 

 ed, arises principally from the two sources, friction upon the axis, and 

 the want of coincidence of the needle's centre of gravity with the axis 

 of motion ; the latter rendering necessary the inversion of its poles. 

 The author suggests a method by which he considers that, probably, 

 the friction may be diminished j but he has principally directed his 

 attention to obviate the necessity of the inversion of the poles. 



In order to remove the practical difficulty attending the adjustment 

 of the centre of gravity to the axis of motion, an operation in which 

 the artist rarely, if ever, completely succeeds, the author proposes to 

 dispense with this condition ; and shows how the dip may then be 

 determined, without the necessity of inverting the poles of the needle, 

 the position of its centre of gravity having been determined previously 

 to its being magnetized. The advantages attending the method pro- 

 posed by the author are not, however, restricted to the determination 

 of the dip with greater accuracy and greater facility : a further and 

 still greater advantage attending the use of a dipping needle on the 

 principle he proposes, is, that a measure of the terrestrial magnetic 

 intensity will be obtained by the same observations which give the 



