OF TERRESTRIAL MAGNETIC FORCE IN THE HORIZONTAL PLANE. 683 
is marked on the curve, there is no difficulty in fixing approximately on the solar 
times corresponding to the extreme N. and S. values, and the exti'eme E. and W. 
values, mentioned above. These are all the elements of the magnetic record which 
are described in the subjoined table. 
The changes in the monthly records are very remarkable. They leave no doubt 
in my mind that the diurnal magnetic changes are produced by the sun. But I 
cannot account for every change that takes place in the course of a day ; nor can 
I undertake to say whether we can found, on these, the theory that general terrestrial 
magnetism is a part of solar radiation, perhaps sometimes acting through or sometimes 
impeded by the masses of land and sea on which that radiation acts. 
Still I think that a considerable step is made by the establishment of a connexion 
between terrestrial magnetism (on one band), and the radiation, or, at least, the 
visibility of the sun (on the other hand). 
