Major-General Sabine on Colonial Magnetic Observatories. 308 
been found competent to determine, with an approximation suffi- 
cient for present theoretical purposes, the character and amount for 
each element of the regular daily effect of the moon on the terrestrial 
magnetic phenomena, the existence of which does not appear to have 
been even suspected at the time when the Report of the Committee 
of Physics wasdrawnup. The discovery of the moon’s influence on 
any of the magnetic elements is due, as already stated, to M. Kreil ; 
but Toronto is the first, and as yet the only, station, at which the 
numerical values at every lunar hour of the lunar-diurnal variations 
of the three elements have been published. Corresponding state- 
ments to that which has been given for Toronto, will be found for 
St. Helena and Hobarton, in the volumes of those observatories, 
which are now in preparation. All the results at the three stations 
present the same general characters. The lunar influence does not 
appear to participate in the decennial inequality which is found in 
all the solar variations (Phil. Trans. 1857, Art. I.). The lunar- 
diurnal variation of each of the elements is a double progression in 
the twenty-four hours, having epochs of maximum and minimum 
symmetrically disposed. In character, therefore, it differs from 
what might be expected to take place if the moon were possessed of 
inherent magnetism, 7. e. if she were a magnet, as it is usually 
termed, per se; and accords with the phenomena which might be 
expected to follow if she were magnetic only by induction from the 
earth. On the other hand, it is believed that the amount of the 
variation, as observed at each of these stations, very far exceeds what 
can be imagined to proceed from the earth’s inductive action re- 
flected from the moon. In this theoretical difficulty we are naturally 
thrown back to seek a more extensive knowledge of the phenomena 
than we have yet obtained, and to the generalization which will follow, 
when sufficient materials for it have been procured. In subordinate 
particulars, a difference, which is apparently systematic, is perceived 
to exist in regard to the hours which constitute the epochs of maxima 
and minima at the three stations, as well as in regard to the amounts 
of the respective variations ; these differences are no doubt intimately 
connected with the causes of the phenomena, and are likely to lead 
to their elucidation. It is therefore greatly to be desired that the 
number of stations furnishing complete determinations, such as the 
Colonial Observatories only have hitherto supplied, should be in- 
creased, 
The domain of periodical variations has thus been considerably 
enlarged since the Report of the Committee of Physics was drawn 
up; and must henceforth be understood to comprise, in addition to 
the variations “‘ whose amount is a function of the hour-angle of the 
sun, and of his longitude” (or of his declination) (Report, p. 10),— 
Ist, those variations of the three elements whose amount is a func- 
tion of the hour-angle of the moon; 2ndly, those variations which 
were classed in the Committee’s Report as “irregular,” or “ appa- 
rently observing uo law,” but which are now known to be governed 
by laws depending on the sun’s declination, and hour-angle ; and 
3rdly, those variations, both “ regular ” and “ occasional,” which 
