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IX. On the Lunar Diurnal Variation of the Earth's Magnetism at Pavlovsk 
and Lola (1897-1903). 
By S. Chapman, B.A., D.Sc., Fellow of Trinity College , Cambridge, and, 
Chief Assistant at the Royal Observatory , Greenwich. 
Communicated by the Astronomer Royal , F.R.S. 
Keceived June 19,—Bead June 25, 1914. 
§ 1. The present paper contains an account of the methods and results of an 
investigation into the lunar diurnal magnetic variations at the observatories of 
Pavlovsk and Pola (1897-1903). This work is part of a larger undertaking, now in 
progress, by which I hope to obtain the data necessary for the discussion of the lunar 
diurnal magnetic variations over the whole earth, using the method of the Gaussian 
potential in a manner similar to that in which Schuster applied it to the solar 
diurnal magnetic variations. For this purpose data will be computed from at least 
three or four other observatories. The labour of computation involved is very large, 
and in the present instance has been executed partly by the aid of a grant from the 
Government Grant Committee of the Boyal Society, and partly by assistance put at 
my disposal by the Astronomer Poyal and Dr. Schuster. While the data thus 
obtained will, I trust, throw much new light on the theory both of the lunar and 
solar diurnal magnetic variations, the investigation has been undertaken not with 
any thought of finality in itself, but rather as an incentive to the provision of data 
for a more accurate and detailed discussion by subsequent workers. The reduction of 
the observations to the required form is, in fact, almost too great a labour for a 
single person to undertake if it is to be done on an adequate scale and in a reasonable 
time. It is in the hope, therefore, that a number of directors of magnetic observa¬ 
tories may be induced to carry out the reductions for their own stations that I have, 
in this paper, indicated what seems to me to be the simplest and most suitable method 
of computation for the purpose, and also some of the lines along which the discussion 
of the results from a single observatory should proceed. In a later paper some 
further points will be dealt with, in addition to the final discussion of the collected 
results from several observatories ; for a general review of the subject, reference may 
be made to my recent discussion of the previously existing data for Batavia, Bombay, 
VOL. COXIV.-A 517. Published separately, September 26, 1914. 
