82 REPORT— 1885. 
VIII. Letter from Sir Frederick Evans to Professor Stewart. 
21 Dawson Place, Bayswater, London, W. : 
May 9, 1885. 
Dear Professor Balfour Stewart,—I shall be glad to render the 
Magnetic Committee all the assistance in my power, but I have been much 
out of sorts in my health for some time, and cannot so well undertake 
any work requiring much application. 
On Tuesday I leave London for a few days, and will take the papers 
with me you forwarded on the 6th instant. 
Until we see our way more clearly, it is the discussion of the dis- 
turbances of the Declination needle which appears to me the most im- 
portant to break ground upon. Ona clear insight of the probable laws 
at a few selected stations in both hemispheres, a discussion of other 
elements might well follow. Too grand a scheme and complicated 
methods of research would, I fear, break down. Sabine’s methods had, at 
least, simplicity to recommend them. 
A letter to the above address will reach me. 
Yours faithfully, 
Frepk. Jno. Evans. 
IX. Letter from the Astronomer Royal to Professor Stewart. 
Royal Observatory, Greenwich, London, §.E. : 
July 8. 
Dear Prof. Stewart,—The printed suggestions for the Committee on 
Magnetical Reductions arrived at a very busy time, and since then I have 
been away from home; hence the delay. 
As there is some difficulty in discussing abstract questions, I think 
it would save misunderstanding if you would make your suggestions with 
reference to our Magnetical Results for 1883, now in the press, of which 
I send youacopy. There are several additions and alterations which I 
have introduced in consultation with Mr. Ellis, in order to give as much 
information as practicable about the magnetic curves. We now give, in 
addition to mean values of the magnetic elements for each day and the 
mean diurnal curves for each month, the daily range, 7.c., the amplitude 
of the diurnal curve for each day, and particulars of all disturbances, 
small as well as large (either in the notes or in the plates). Harmonie 
analysis also has been applied to the diurnal variations for each month 
and for the year. 
Now the question is, how far the suggestions of the Committee are 
carried out in the results given. As for rejection of disturbances, I am 
inclined to agree with Sir Henry Lefroy in his objection to Sabine’s 
mode of treatment. At Greenwich the practice has been to draw @ 
pencil curve smoothing down the irregularities of the trace, and to reject as 
disturbed those days for which a continuous pencil curve, agreeing gene- 
rally in form with the normal curve, could not be drawn through the trace. 
I see no reason to modify this. 
Yours very truly, 
W. H. M. Curistiz. 
