23 
Ordinary Meeting, November 16tb, 1886. 
Professor Osborne Keynolds, LL.D., F.RS., Vice-President, 
in the Chair. 
“ The Application of the Harmonic Analysis to the Regular 
Solar Diurnal Variations of Terrestrial Magnetism,” by 
Charles Chambers, F.R.S., Superintendent of the Colaba 
Observatory, Bombay; communicated by Professor Balfour 
Stewart, LL.D., F.R.S. 
The great virtue of the harmonic analysis, as applied to 
terrestrial magnetism, lies in its taking the facts of nature 
as they stand — ^discarding none because they have a seeming 
complexity, and selecting none because they have a seeming 
simplicity — and weaving them all into a definite system, 
which the mind is capable of grasping as a whole : its 
application substitutes, as a subject of contemplation, for 
distributions on the earth's surface of, say, three sets of 
components of force, or of a single resultant force and its 
two directions, obtained directly from observation, an 
equivalent distribution of potential and the forces related 
thereto. 
The mathematical expression for the potential having the 
form of an indefinite series of terms of increasing degree, 
its agreement with observation will be closer the higher the 
degree at which the expression stops ; and increasing diffi- 
culties and complexity of calculation alone, fix a limit to the 
degree of the last term, which should be included. To select 
a particular subordinate term of any one degree, and call 
that the potential, might well be to evolve from the imagi- 
nation an interesting exercise, but would obviously be to 
ignore the fundamental character of the potential in a case 
PEOCEEDixas— L it. & Phil. Soo.—Vol. XXYI.—No. S.—Session 1886-7. 
