PROGRESS OF MAGNETIC THEORY. 231 



o-ations I have been describing belong to the mechanical side of the sul- 

 ject : but when philosophers have to consider the causes of the secular 

 changes which are found to occur in this mechanical condition, they 

 cannot fail to be driven to electrical, that is, chemical agencies and laws 



I can only allude to Gauss's investigations respecting the Absolute 

 Measure of the Earth's Magnetic Force. To determine the ratio of 

 the magnetic force of the earth to that of a known magnet, Poisson 

 proposed to observe the time of vibration of a second magnet. The 

 method of Gauss, now universally adopted, consists in observing the 

 position of equilibrium of the second magnet when deflected by the first. 



The manner in which the business of magnetic observation has been 

 taken up by the governments of our time makes this by far the 

 greatest scientific undertaking which the world has ever seen. The 

 result will be that we shall obtain in a few years a knowledge of the 

 magnetic constitution of the earth which otherwise it might have 

 required centuries to accumulate. The secular magnetic changes 

 must still require a long time to reduce to their laws of phenomena, 

 except observation be anticipated or assisted by some happy discovery 

 as to the cause of these changes. But besides the special gain to 

 magnetic science by this great plan of joint action among the nations 

 of the earth, there is thereby a beginning made in the recognition 

 and execution of the duty of forwarding science in general by national 

 exertions. For at most of the magnetic observatories, meteorological 

 observations are also carried on ; and such observations, being far 

 more extensive, systematic, and permanent than those which have 

 usually been made, can hardly fail to produce important additions to 

 science. But at any rate they do for science that which nations can 

 do, and individuals cannot ; and they seek for scientific truths in a 

 manner suitable to the respect now professed for science and to the 

 progress which its methods have made. Nor are we to overlook the 

 effect of such observations as means of training men in the pursuit of 

 science. " There is amongst us," says one of the magnetic observers, 

 " a growing recognition of the importance, both for science and for 

 practical life, of forming exact observers of nature. Hitherto astro- 

 nomy alone has afforded a very partial opportunity for the formation 

 of fine observers, of which few could avail themselves. Experience 

 has shown that magnetic observations may serve as excellent training 

 schools in this respect." ie ] 



18 Letier of W. Weber. Brit. Assoc. Rep. 1845, p. 17. 



