37 
that it would be highly injudicious to attempt it with crude 
raw material. A considerable work of collation and evalu- 
tion of the available results of observation has first to be 
carried out, and it would be a culpable yielding to impa- 
tience to expend funds upon elaborate calculations, until 
something was known of the probable errors of the data on 
which such calculations would have to be based. That 
there is necessity for magneticians, who have the respon- 
sibility of directly or indirectly advising the Government on 
magnetic matters, to be on their guard, is evident when we 
find Dr. Schuster lightly suggesting that two or three 
declination magnetographs should be distributed over the 
northern frontier of India and one additional vertical force 
instrument be placed in Central India — even when they 
are to be worked only for a single year. 
Bemarks on Mr. Chambers’ paper entitled : The 
Application of the Harmonic Analysis to the Begular Solar 
Diurnal Variations of Terrestrial Magnetism,” by Professor 
Akthur Schuster, Ph.D., F.R.S. 
Mr, Chambers has done me the honour of reading my 
paper on the diurnal variation of terrestrial magnetism, and, if 
I understand him correctly, he has met with some difficulties, 
which he desires to have explained. Mr. Chambers has 
done excellent work as a practical magnetician, and I am 
naturally anxious that he should be clear about the methods, 
by means of which, in my opinion, all magnetical observa- 
tions will have to be reduced. It is for this reason only, 
that I shall enter into a discussion of the questions he 
raises. 
In the first part of my paper I tried to show that, except 
perhaps in the arctic regions, we are justified in assuming 
the existence of a potential on the surface of the earth for 
the variable part of the magnetic forces. I derived an 
