in the position of the horizontal needle , &c. 131 
Mr. Christie, in pursuing the experiments above referred 
to, and in those on the effects of temperature on magnets, 
had made use of an instrument admirably suited to such 
purpose ; and he very obligingly superintended the construc- 
tion of one somewhat similar for my use ; a description and 
drawing of which he has given in his paper on the effects of 
temperature on magnets, published in the Phil. Trans, for 1825. 
In these experiments, the apparatus was frozen to three 
firm stone supports, erected in a house built of snow, having 
the top covered with canvas ; the zero on the compass- 
box was made to coincide with the direction of the needle 
at 6 b A.M., that being, although somewhat arbitrarily con- 
sidered (from the mean of the preceding month’s obser- 
vations on the daily variation), the magnetic meridian. The 
needle used was made of clock spring, very delicate and 
light, in length 4,5 inches, its greatest breadth at the centre 
was 0,45 inches, and its extremities terminated in sharp 
points ; the pivot on which it rested was also repolished pre- 
vious to the commencement of the observations. 
Having considerably reduced the directive power of this 
needle in its natural direction, by the action of two bar mag- 
nets, placed in the magnetic meridian, and in the same hori- 
zontal plane with it ; I began on the 14th of February to 
register the amount of the daily change at stated intervals 
throughout the twenty-four hours, the Officers of the ship 
kindly assisting me, by taking the observations at the times 
of my attendance to other duties. The states of the two 
thermometers placed upon the instrument, were also noted 
at the time of every observation ; and to preserve the inten- 
sity of the magnets from being affected by any sudden change 
