INTRODUCTION AND RESULTS. 
243 
of the United States at stations of the Coast Survey, and which will hereafter be pub- 
lished in the Government reports. In the mean time the results have been communi- 
cated to me by Dr. Bache, with the permission of the Government. 
I have also availed myself of the Inclinations observed in different parts of the 
United States, by Professor Loomis and M. Nicollet, published in the seventh and 
eighth volumes of the Transactions of the American Philosophical Society. The 
skill of these gentlemen as observers, and the scrupulous care with which their ob- 
servations are recorded, are too well-known to require comment. 
In conformity with the plan adopted in former numbers of these Contributions, 
I shall now proceed to discuss the general results of the observations embodied in 
this memoir under the separate heads of Magnetic Force and Inclination; referring 
where necessary to the documents in the sequel. 
Magnetic Force. 
The statical observations of the total Force furnish determinations at 120 stations, 
at /3 of which Lloyd’s needles were employed, and Fox’s needles at 109 stations. 
The observations of the horizontal force, with the magnets of the portable magneto- 
meters, furnish determinations at 57 stations. The statical and horizontal methods 
together comprise 140 stations : the observations are given, and the results deduced in 
§11. To these we have to add 10 determinations made at 10 stations near New York 
by Mr. Renwick, with a portable unifilar ; and the ratios of the horizontal force at 
101 stations, chiefly in the United States, by Dr. Locke, with a Hansteen’s apparatus 
in which the needles vibrated in a partial vacuum. The connection of Dr. Locke’s 
observations with those of Lieut. Lefroy, has been established by means of eleven 
stations common to both series, enabling both to be expressed in a common unit. 
The general table, No. XLVIII., which concludes §11, comprehends 288 determina- 
tions of the magnetic force at 234 stations. Of the determinations 32 are of the 
absolute horizontal force, in which the magnetic moments of the magnets employed 
were examined on the spot: 35 were obtained with the same magnets, and give also 
the absolute horizontal force, but the magnetic moments were computed for the sta- 
tions from experiments of deflection at other stations : 101 are of the ratios of the hori- 
zontal force, observed with needles whose magnetism was proved to be constant by 
their having been frequently brought back and examined at a base station; and 120 
are ratios of the total force obtained by the statical method, in which also the mag- 
netism of the needles was proved by their having been brought back to abase station. 
The number of stations at which statical ratios only were obtained is 74 ; the number 
at which horizontal ratios only were observed is 85 ; the number of the stations of 
absolute horizontal determinations only (whether by vibrations and deflections, or 
by vibrations alone) is 29 ; and finally, there are 37 stations at which both absolute 
and relative determinations were made. 
As all the stations of relative determination have the observatory at Toronto as a 
