Royal Society, 46t 



Temperate Zone," separately printed from the * Memoirs of the Roy. 

 Soc. of Sciences of Copenhagen,' By calculating newer and more 

 ancient observations of the magnetical declination, I have ascertained 

 the movement of the four magnetical polar regions, which T had 

 already found in my work ' Untersuchungen liber den Magnetism us 

 der Erde' (Christiania, 1819, with Atlas) ; whereof the two northern 

 ones have a motion from west to east, the two southern ones in the 

 contrary direction ; and have attempted thereby in general to declare 

 the cause of the known variations, as well of the system of declina- 

 tion as of that of inclination and of intensity. 



As I am indebted for the greatest part of the materials to English 

 observations, I have found it my duty to render my thanks to 

 English science, and to express my hopes of future exertions towards 

 the solution of this, in my thought, most interesting problem of the 

 general physics of the globe. 



Most respectfully. 



Observatory in Christiania, CHRISTOPHER Hansteen. 



December 31, 1855. 



March 6. — Colonel Sabine, R.A., V.P. and Treasurer, in the Chair. 



The following communications were read : — 



" Supplement to the * Account of Pendulum Experiments under- 

 taken in the Harton Colliery;' being an Account of Experiments 

 undertaken to determine the correction for the Temperature of the 

 Pendulum." By G. B. Airy, Esq,, Astronomer Royal. 



Adverting to the circumstance that, in the Harton Experiment, 

 there was a mean difference of 7° between the temperature above and 

 below, and that a careful determination of the coefficient for tem- 

 perature-correction was therefore necessary, the author describes the 

 process by which the correction was now investigated by experiment 

 on the same pendulums which were used in the Harton Experiment. 

 Two rooms were selected at the Royal Observatory, Greenwich, 

 having firm stone floors, and admitting of being heated, one by a 

 stove in the room, the other by a hot-air-apparatus below. One 

 pendulum was mounted upon its iron stand, with clock and other 

 apparatus, in one room, and the other in the other room. Care was 

 taken that the pendulums and their thermometers should be effec- 

 tually protected from radiation. The two clocks were compared by 

 carrying a chronometer from one to the other, and remarking the time 

 of coincidence of beats ; a method which admits of very great accu- 

 racy, when (as in this instance) the distance through which the 

 chronometer is to be carried is small. In the Fifth Series (counting 

 the series in sequence to those of the Harton Experiment), Pendulum 

 1821 was kept in heat, and Pendulum 8 cool, and continuous obser- 

 vations were kept up during forty hours. In the Sixth Series, Pen- 

 dulum 8 only was kept in heat, and observations were again kept 

 up during forty hours. The Seventh and Eighth Series were similar, 

 respectively, to the Fifth and Sixth. The temperatures are referred 

 to two of the thermometers used in the Harton Experiment, and to 

 two other thermometers supplying the place of two of the Harton 



