PROGRESS IN SCIENCE IN TERRESTRIAL MAGNETISM. 337 
or waves of changing magnetism, or lashed into furious 
magnetic stormsand we may add that, in our present state 
of knowledge, the causes of all these changes are associated 
with an indefinable something, which, like an undetected 
planet, we recognize by its workings, though unable as yet 
adequately to describe. 
Let us then look back for a moment and see the steps by 
which we have ascended from the lodestone—by the dis¬ 
covery of the declination and inclination, by the grand con¬ 
ception of Gilbert, by the labors of Halley, Hansteen, and 
Sabine, and by the mathematical genius of Gauss—up to 
the threshold of the era in which we see clearly that the 
office which we have to perform in order to effect definite 
progress in the science of terrestrial magnetism is to dis¬ 
cover, by scientific measurement, the observational facts of 
the direction and intensity of the Earth’s magnetic force, 
both over the land and over the sea, in every part of the 
world. 
