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XXII. On the Lunar-Diurnal Magnetic Variation at Toronto. 
By Major-General Edward Sabine, R.A., D.C.L., Treas. V.P.R.S. 
Received June 13, — Read June 19, 1856. 
In fulfilment of an intention expressed to the Royal Society in November 1853*, I 
have now the honour to submit to the Society the results of an investigation into the 
Moon’s diurnal influence on the horizontal and vertical components of the magnetic 
force at Toronto, and the consequent deduction of the Lunar-diurnal Variations of 
the Inclination and of the Total Force at that Station. 
The processes to which the observations of the Bifilar and of the Vertical force 
Magnetometers, as received from Toronto, were subjected after their arrival at Wool- 
wich, with a view to this and to other investigations, have been already partially 
described in a communication presented to the Society in a former part of the present 
Session'!'. The processes there described had reference particularly to the reduction 
of the observations to a uniform temperature of the magnets employed to measure 
the variations of the respective components of the force, — to the elimination of the 
larger disturbances, — to the formation of normal values (omitting the disturbances) 
for each of the components at every hour of mean solar time for periods usually of a 
month’s duration, — and to the deduction of the solar-diurnal variation in different 
years and different months, after the larger disturbances had been eliminated. 
The investigation regarding the Moon’s influence was commenced by marking 
every observation in small figures on the face of the monthly tables with the lunar 
hour to which each observation most nearly corresponded. This was done in the 
manner described in the second and third pages of Art. XIX. in the Philosophical 
Transactions of 1853, when treating of a similar process in the case of the Magnetic 
Declination. A fresh set of monthly tables were then prepared for every month in 
each of the five years, in which tables were entered the differences, each under the 
lunar hour to which it most nearly corresponded, between the several observations 
and their corresponding normals. By this proceeding the diurnal and other varia- 
tions depending on the time of the solar year, and on the hour of the solar day, were 
in great part at least eliminated. The differences were marked with a + or a — 
sign, according as the amount of the force at the time of the observation was greater 
or less than the monthly normal at the same hour. The mean was then taken in 
every month of every lunar hour (attending to the signs), and the monthly means 
were collected into yearly means. The lunar hour to which each observation most 
* Philosophical Transactions, 1853, Art. XIX. t Ibid. 1856, Art. XVI. 
MDCCCLVI. 3 U 
