PRESIDENT’S ADDRESS. 167 
There is consequently some reason to hope that amateur activity 
may in the immediate future render valuable services in some of 
these classes of astronomical observations in which the Government 
Observatories are unable to take an active part. 
Enough has been said, I think, to show in what direction 
these colonies may co-operate in the best interests of astronomy 
in proportion to their resources and circumstances. 
I will now invite your attention to certain subjects of Terres- 
trial Physics, which derive their great importance, not only from 
purely scientific considerations, but from their more or less direct 
bearing upon our material interests, and also, from the fact that in 
very recent years, and at the present time, they have been taken up 
with renewed vigour and determination in the hope of improving 
our knowledge on many points which still remain unexplained. 
Prominent among these subjects is Terrestrial Magnetism. 
Nearly 300 years ago, Gilbert advanced his great theory “ Mag- 
nus Magnes ipse est Globus Terrestris,” to account for the observed 
phenomena of the freely suspended magnetised needle. 
To this day science has not heen able to determine absolutely 
whether this theory can be finally accepted as true. 
Another theory is that which regards the earth’s magnetic field 
as an induced one, ascribed to the action of electric currents cir- 
culating within the earth’s crust. 
But whether the earth acts as a great magnet, or as a great 
electro-magnet, science is as yet unable to tell. As Dr. Bauer 
puts it, no satisfactory answer has as yet been given to the question 
“Ts the earth’s magnetism permanent, or induced ?” 
Still more remote seems to be the probability of discovering the 
origin of the earth’s magnetism, and the cause of its variations 
and perturbations. Magnetic phenomena, as they occur on the 
earth’s surface, appear to be related to solar activity, atmospheric 
electricity, and possibly to other meteorological conditions, but the 
nature of these relations is not known. 
These are large theoretical problems awaiting solution in the 
immediate future. 
It has been urged that more systematic and careful observations 
of earth’s currents should be made, as a part of the regular work 
of magnetic observatories, and that magnetic exploration of the 
atmospheric layers, and of the bottom of the sea, is as necessary as 
the exploration of the earth’s surface for the solution of these 
questions. 
Of more practical importance, however, is the knowledge of the 
distribution of the earth’s magnetism, and of the laws which 
govern its variations ; for it is this knowledge that enables mag- 
neticians to construct those magnetic charts which are of so great 
a service to navigation and to land surveying, especially in new 
countries. 
