ON COMPARING AND REDUCING MAGNETIC OBSERVATIONS. 65 
Report of the Commvittee, consisting of Professor BALFoUR STEWART 
(Secretary), Sir W. Tuomson, Sir J. H. Lerroy, Sir FREDERICK 
Evans, Professor G. H. Darwin, Professor G. CHRYSTAL, Professor 
S. J. Perry, Mr. C. H. CarpmMaet, and Professor SCHUSTER, 
appointed for the purpose of considering the best means of 
Comparing and Reducing Magnetic Observations. Drawn wp 
by Professor BALFOUR STEWART. 
Iy presenting their report to the British Association the Committee 
would begin by referring to the appendix, in which are embodied sug- 
gestions of great value which they have received from men of science at 
home and abroad. The Committee desire to express their thanks to the 
authors of these contributions. 
While a final discussion of these communications cannot be attempted 
in this first report, it is nevertheless evident that magneticians are not 
agreed as to the best method of determining absolutely the solar-diurnal 
variations of the three magnetic elements—that is to say, the diurnal 
variation resulting after the elimination of all disturbed observations. 
The point in dispute is the method of distinguishing and separating the 
disturbed from the undisturbed observations. On the whole, the feeling 
is against the method of Sabine, on account of the arbitrary nature of his 
separating value. 
An alternative method has been proposed by Dr. Wild, Director of the 
Central Russian Observatory (Appendix, No. VII.). This method seems 
to be in some degree analogous to that pursued at Greenwich (Appendix, 
No. IX.). Dr. Wild selects those curves which appear to the eye to be 
free from the short-period irregularities characteristic of disturbances, 
and considers the results obtained from their measurement to embody a 
trustworthy representation of the solar-diurnal variation for the time and 
place in question. He finds a remarkable uniformity and simplicity of 
type in the variation as given by the different selected curves. 
While the Committee recognise in this a method which may ultimately 
meet with general acceptance, they think there are various points con- 
nected with it which require investigation. 
In the first place, it would be desirable to prove, by means of an 
exhaustive discussion of some one element—as, for instance, the declina- 
tion—to what extent curves selected by the eye do, as a matter of fact, 
present this uniformity and simplicity of type. 
There are abundant materials available for this purpose at the Kew 
Observatory, and it is hoped that through the kindness of the Kew 
Committee this point may eventually be settled. 
Again, it would be desirable to ascertain whether the apparently 
normal days at one station coincide with those at another; and, if so, 
whether there is a definite or nearly definite relation in type and range 
between the corresponding smooth curves of two widely separated stations 
of not very dissimilar latitude. 
_ This point will form one of the subjects of a discussion undertaken by 
Sir J. Henry Lefroy, who proposes to compare the curves of Toronto and 
ae oe together for the years 1849-53. 
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