80 



In conclusion, it may be useful to call the attention of the Society, 

 and of those Fellows in particular who interest themselves in tracing 

 up the phenomena of nature to their physical causes, to the assem- 

 blage of facts which are now available for such inquiries, in a branch 

 of magnetical science which may not inappropriately be called 

 celestial magnetism. In the introductory discussion prefixed to the 

 2nd volume of the St. Helena Magnetical Observations, p. cxliv to 

 cxlvidi, the lunar-diurnal variation is given for each of the three 

 magnetic elements, the Declination, the Dip, and the Intensity of the 

 force, at the four stations of Toronto, St. Helena, the Cape of Good 

 Hope and Hobarton, and for the Decimation at two additional stations 

 Kew and Pekin. The variations are given both in formulae and in 

 tables ; the latter exhibiting the amount of the lunar influence at 

 each of the 24 lunar hours, in the several magnetic elements at each 

 station. These data are directly applicable to inquiries into the 

 nature of the moon's magnetism ; and into the mode by which the 

 moon's magnetism acts either on the magnetism of the earth itself, 

 or on the magnetic needle stationed at different points of the earth's 

 surface, so as to produce a small but systematic and perfectly ap- 

 preciable variation in each of the magnetic elements, having a double 

 period in every lunar day. 



The lunar-diurnal variation of the Declination at Kew and Ho- 

 barton, as given in this communication, is slightly different from the 

 figures in the 2nd St. Helena volume referred to, because the results at 

 Kew are a mean of 3 years instead of 2, as in the St. Helena volume ; 

 and at Hobarton a lower standard has been taken for the disturb- 

 ances, causing a larger number of the disturbed observations to be 

 omitted in the calculation of the lunar-diurnal variation. 



