yi6 Royal Society. 



He then details a set of experiments by which he assured himself 

 that a uniformity of action obtained wherever in the circumference 

 the heat was applied. He next instituted a series of observations 

 for determining the laws which govern the magnetic phfcnomena 

 resulting from the application of heat as above described ; the re- 

 suits of which are stated in the form of tables. 



Four poles appear to be produced, two north and two south, the 

 north both lying in one semicircle, and the south both in the other, 

 and not in alternate quadrants, and all the poles lying rather nearer 

 to the centre than the line of junction of the two metals. The 

 experiments were pursued in a variety of positions of the plate with 

 respect to the meridian and horizon, and with a similar general re- 

 sult. 



From these experiments the author concludes that uniformity of 

 junction of the two surfaces of a thermo-raagnetic combination is 

 no obstacle to the development of transient polarity. Regarding 

 the earth and its atmosphere as such a combination, and limiting 

 our views to the intertropical zone alone, we should have two mag- 

 netic poles produced on the northern, and two on the southern sides 

 of the equator, the poles of opposite names being diametrically 

 opposite to each other. 



To apply this to the earth, it is necessary to know the times of 

 greatest heat in tlie twenty-four hours : this may be assumed at 

 three o'clock in the afternoon. The apparatus used by the author 

 not affording, when adjusted to the latitude of the place, sufficient 

 magnetic power to render the effects distinct, he substituted for it 

 an artificial imitation consisting of two magnets, six inches long, so 

 placed with resfiect to a revolving axis parallel to the axis of the 

 earth, as to imitate the position of the poles produced by thermo- 

 magnetism in his plate, and making the apparatus revolve round 

 this axis, he noticed the deviations produced thereby on a compass, 

 placed horizontally over it. These deviations he then compares at 

 length, with those actuall)' observed first by Lieut. Hood, in 1821, 

 at Fort Enterprize, lat. 61° 28' N. ; 2dly, by Canton, in London, in 

 17.59 ; 3dly, by Lieut. Foster, at Port Bovven, in 182,') ; 4thly, by 

 Col. Beaufoy, on Bushy Heath, in 1820. The results of this com- 

 parison are on the whole, generally such as to indicate a conformity 

 between the hypothesis and fact, with the exception of some de- 

 viations from the exact times of maximum and minimum variation 

 which could not but be expected. 



The author then considers the manner in which the distribution 

 of land and sea over the globe modifies the point of greatest heat, 

 and in consequence the place of the diurnal poles. He next ob- 

 serves, that at the commencement of the experiments, he had no 

 idea of being able to reduce the deviations of the needle to so sim- 

 ple a law as that resulting from a polarity in a particular direction 

 communicated to the plate ; but that he considered it of the greatest 

 consequence, to ascertain whether the deviations on the outer 

 edge of his plate, had the same general character with those within, 

 at the time of junction of the metals ; since these situations of the 



needle 



