66 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVI.) 
2923. The case may be more simply stated, for the facility of recollection, by saying 
that the effect of the sun is to raise the magnetic curves, over the equatorial and neigh- 
bouring parts, from their normal position, in doing which the north and south dip 
are simultaneously affected and increased. 
2924. At the place d like effects on the inclination must be produced, and theo- 
retically it should be affected in the same direction even at N. and S. At the 
point a the inclination is supposed to be not at all altered, but going either north or 
south, the changes appear and increase. It is not probable that the maximum al- 
teration will be at N. or S., but the latitude where it will occur must depend upon 
the many conjoined circumstances that belong to the case of a globe round which a 
magnetic lens, such as I have endeavoured to describe, is continually revolving. 
2925. Instead of assuming that the sun is at H, let us suppose that we are looking 
at the diagram in a vertical position and towards the east ; the sun coming up from 
the east and passing over our heads, and bringing with it that condition of our atmo- 
sphere which is the cause of the change. As it does so, all the magnetic curves would 
rise ; the inclination would increase at b, d, and every place where there was any before- 
hand, in opposite directions on the two sides of a ; this would go on until the sun was 
in the zenith, and then as it passed away and sank behind us, the lines would draw 
in again and the dip diminish to what it was at first. The m.aximum of dip would be 
when the sun was near the zenith, and the minimum when he was quite away. 
2926. But if the resultant of force be above in the atmosphere (2937.)? which is 
by far the most probable, as it is the whole atmosphere which acts by heat diamag- 
netically, then the results would be modified ; for if over a the lines of force might 
be depressed, and the inclination there would be diminished ; at Z/ it might not for the 
moment be affected ; whilst in higher latitudes it would be increased, according as the 
line of force from the resultant in the atmosphere, wherever that might be, fell out- 
side of the angle formed by the inclination with the horizon of a given place or within 
it. St. Helena, the Cape of Good Hope and Hobarton, furnish instances of the three 
cases. 
2927. At the same time the total force would undergo a change in its amount ; that 
transmitted through a given space would be least when the sun was in the zenith, 
and most when he was away (2863.). The total variation in the force should be 
greatest at a, and diminish from thence towards north and south. The daily variations 
of the inclination are so imperfectly known to us at present, that we cannot say how 
far the natural changes will accord with these expected variations, but as far as the 
observations go they agree with the theory. 
2928. If the sun, instead of being over the equator, is at a tropic and so vertical, 
for instance over h, then the effects will be modified ; and the resultant still being 
assumed as above, the lines of force which before were not affected, may be expected 
to descend and lessen the inclination, whilst other lines in higher latitudes, which 
before were increased in inclination, may now be but little affected, and other lines 
