OBSERVATIONS OF THE MAGNETIC FORCE. 
271 
polish of the axle was found perfectly good, but the back axle had been injured in 
shape. A spare axle had been furnished with the apparatus, and appearing per- 
fect both in shape and polish, it was fitted to F. C., and observations were made with 
this needle at Norway House on the 11th of August 1843, and were repeated at the 
same spot on the /th of September 1844. The magnetism of the needle appeared 
steady, but from some undiscovered cause its performance at some other stations at 
which it was tried was sluggish and irregular, so that no satisfactory results were 
obtained with it at them. On the return to Toronto, the angles of deflection were 
observed with the same weights which had been used at Norway House in August 
1843 and September 1844. These give an identical value for the increase of the 
magnetic force between Toronto and Norway House, to that obtained by the other 
needle of the apparatus F. A. ; the particulars are given in Table XVII. 
In Mr. Fox’s apparatus the angle of deflection with any particular weight is half 
the difference of the arcs shown with the weight first on the one hook, and then on 
the other hook. The experiment is repeated with the face of the circle both east and 
west, and the angle of deflection entered in the Table is the mean of the angles with 
the face of the circle east and west. 
L. A. and L. B. were the needles on Dr. Lloyd’s statical principle fitted to the 
Gambey’s circle; at Toronto, in January and February 1843, the observations were 
made with them in Table X., by which the coefficient in the temperature correction was 
determined ; and angles of deflection with weights inserted in the hole most distant 
from the axle were observed for the purpose of supplying a base determination. On 
arriving at St. Helen’s, however, the angles of deflection appeared inconveniently 
large, and the weights were shifted in each needle into the middle hole, and a new 
series of relative determinations commenced. The angles of deflection having been 
observed on the same day at St. Helen’s with the weight both in the middle and in 
the outer hole, the second series become thereby connected with the former ; but the 
advantage of the frequent repetition which had been made at Toronto as a base 
station was impaired, inasmuch as the connection of the second series commencing 
at St. Helen’s is established by a single observation only in each position of the 
weights. On arriving at Fort William at the end of May, it was found necessary 
again to change the weights, because the view of the part of the circle opposite to 
which the needle rested was interrupted by the cross bar which supports the agate 
planes. In the case of L. B., the weight was now replaced in the hole in which it had 
been used at Toronto, and the connection of the subsequent observations with the 
original base station was thereby fully restored. In the case of L. A., a new weight 
appears to have been chosen, and as observations were made at Fort William both with 
the old and the new weight, the two series with this needle,— viz. before and after 
the change of the weight at Fort William, — have that station common to both. From 
the time of the embarkation in the Hudson’s Bay Company’s canoes at La Chine, 
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