REPORT— 1854. 
366 
In speaking of the lunar magnetic influence, however, it is proper to pre¬ 
mise that the Colonial Observatories cannot claim the distinction of having 
been the first to make it known ; although it is probable that the knowledge 
which has been gained by their means, of the different effects which the 
moon's magnetic influence produces in different parts of the earth, cannot but 
contribute in a very material degree to that generalization of the phenomena 
to which wo must look before we can expect to hare a satisfactory know- 
ledge of wlmt the moon's magnetic state is. Without entering into parti¬ 
culars, for which this would be an unsuitable occasion, I may perhaps see- 
ceed in acquainting you by n few words with the method by which another 
of our associates, M. Kreil, Director of the Magnetic Observatories, first at 
Milan and afterwords at Prague, and now Superintendent of the Magnetics! 
and Meteorological Establishments in the Austrian States, succeeded in 
tracing the existence of the lunar influence of which >ve nro speaking, and 
which, with some modifications, I have also employed for a similar investiga¬ 
tion of the observations collected at the Colonial Stations. The method, 
as employed for the Colonial Observatories, is as follows!— The precise 
direction to which the magnet points is observed, ns I have already 
noticed, at every hour. These are hours of solar time, and differ from 
hours of lunar time, inasmuch as the moon takes, on the average, about 
24 hours and 40 minutes of solar time from her passage of the meridian on 
one day to her passage of tho meridian at the same place on the next day. A 
lunar hour is therefore somewhat longer than a solar hour, and observations 
made at regular intervals of Solar time do not exactly correspond toanyregular 
scries of lunar hours. But the twenty-four observations made in the coupe 
of a solar day may be so arranged that each observation may be placed in 4 
tabic under the lunar hour to which it is nearest in point of time; am*i® 
this arrangement the greatest error that can take place iu the classification of 
the observations, according to their corresponding nearest lunar hour, will not 
in any case exceed 30 minutes. If therefore the whole of the hourly obsena- 
tions for several years are thus arranged, a mean of the observations at each 
lunar hour, taken for each lunation or period of about twonty-eight days, or 
for several such periods combined, will show the relative direction of t|> e 
magnet at each of the 24 lunar hours, or say at 0 hours when she is ou the 
upper meridian, at 12 hours when she is on the meridian below the p#' f j 
at 6 hours and 18 hours when she is 90° on either side of the meridian, m 
at the intermediate hours when she corresponds to the intermediate hour- 
angles. Now when this is done, and the results during several lunations are 
grouped together, so that disturbing influences from other causes Pity J* 
more effectually counterbalanced, and thereby eliminated, the mflg«<' tl ’ 
direction is found to undergo a regular and systematic change iu the coo*’ 
enn«h- nf r ^ hav,n * *"<> *POohs of greatest easterly-pointing ^ 
epochs of greatest westerly-pointing between each two successive pa*ag^ 
eonti?,? ' 0ver , the meruJ,an of the Station, the change in the direction 
t«r.: d :ts“ ,vo from aie ««*«« * ****• 
° < * he difl ' erent '° -"lor and lunar ti* *• ^ 
i„ 5™5£ r f lunar hours must include every varlt 'l 
upon solar hours h , 9 ° ar '" urs am * consequently feV ery variation depend 'j 
after the sohr < C ? nif ‘ K . ct f n, P‘ !ns ^ted ; or the observations may be u*' 
eliminated. ' a varlat,on as w ell as the larger disturbances have b 
worth advertingP ecu ! iarities in this lunar diurnal variation which 
b even in so general and cursory a notice as the pr® 8 ® 11 
