270 
MAGNETIC SURVEY IN NORTH AMERICA. 
On the 28th of October, the needle F. A. being put away in its case, a very powerful 
bar magnet was inadvertently laid on the top of the case for a few minutes. Obser- 
vations made on the following day (the 29th), compared with those which had 
been made on the 26th, showed that the needle had sustained a sensible loss of mag- 
netism by this accident. A new series therefore in the determinations with this 
needle was commenced on the 29th of October, referring to Toronto as a base station, 
at which the value of the force is expressed by 1836 as before. In November 1842, 
F. A. was employed by Lieut. Younghusband, R.A. at four stations in the states of 
Ohio and Michigan, and was brought back to Toronto in the same month : the 
abstract of these observations is given in Table XIII. In the first three months of 1843 
the observations were made in high and low temperatures, by which the coefficient 
in the temperature correction was determined ; and repetitions were made on different 
days in natural temperatures of the angles of deflection with several weights which 
were afterwards employed in the countries to the north. Towards the end of April 
Lieut. Lefroy embarked at La Chine in the canoes of the Hudson’s Bay Com- 
pany, and commenced a course of observations, which was continued daily with very 
few intermissions until his arrival at Athabasca towards the end of September, at the 
conclusion of the season of navigation. The observations with F. A. were made by- 
Lieut. Lefroy himself until the station of the 11th of May at the Trou Portage; 
and from thenceforward by Bombardier Henry, unless where specially noticed in the 
column of remarks in Tables XIV., XV. and XVI. ; towards the end of July the 
performance of the needle was thought to be somewhat impaired, and in consequence, 
at York Factory, the terminations of the axles which worked in jewels, as well as the 
jewels themselves, were carefully examined with a microscope ; the front axle was 
found in admirable order, but the polish of the back axle was not good on one side. 
The jewels were in good order ; the front jewel was scratched on the face and round 
the edge of the cylindrical bore, probably by the end of the axle in mounting the 
needle, but the scratches did not appear to enter the bore or affect the bearing points ; 
F. A. was continued in constant use until the end of the season, but its performance 
was occasionally sluggish and unsatisfactory in comparison with what it had formerly 
been, and led to its being only occasionally employed in the following year. On 
the return to Toronto at the close of 1844, the observations were repeated with the 
weights which had been used in the north ; the performance of the needle on that 
occasion was considered to be a decided improvement on former ones, and the 
angles of deflection agreed within limits of ordinary error with the angles ob- 
served in 1843, before the journey to the north ; showing that the magnetism of the 
needle had sustained no deterioration . during the interval. The abstract of the 
observations with this needle from 1842 to the close of 1844, are given in Tables 
XIV., XV. and XVI. 
Needle F. C. had been kept in reserve at the different stations of the Survey whilst 
F. A. continued to give satisfactory results. Being examined at York Factory, the 
