INTRODUCTORY LECTURE ON EXPERIMENTAL PHYSICS. 245 



scientific value of a combined effort to be made by the observers of all nations, 

 to obtain accurate measurements of the magnetism of the earth ; and we owe 

 it mainly to his enthusiasm for science, his great reputation and his wide- 

 spread influence, that not only private men of science, but the governments of 

 most of the civilised nations, our own among the number, were induced to 

 take part in the enterprise. But the actual working out of the scheme, and 

 the arrangements by which the labours of the observers were so directed as to 

 obtain the best results, we owe to the great mathematician Gauss, working along 

 with Weber, the future founder of the science of electro-magnetic measurement, 

 in the magnetic observatory of Gottingen, and aided by the skill of the 

 instrument-maker Leyser. These men, however, did not work alone. Numbers 

 of scientific men joined the Magnetic Union, learned the use of the new instru- 

 ments and the new methods of reducing the observations ; and in every city 

 of Europe you might see them, at certain stated times, sitting, each in his 

 cold wooden shed, with his eye fixed at the telescope, his ear attentive to the 

 clock, and his pencil recording in his note-book the instantaneous position of 

 the suspended magnet. 



Bacon's conception of " Experiments in concert " was thus realised, the 

 scattered forces of science were converted into a regular army, and emulation 

 and jealousy became out of place, for the results obtained by any one observer 

 were of no value till they were combined with those of the others. 



The increase in the accuracy and completeness of magnetic observations 

 which was obtained by the new method, opened up fields of research which 

 were hardly suspected to exist by those whose observations of the magnetic 

 needle had been conducted in a more primitive manner. We must reserve for 

 its proper place in our course any detailed description of the disturbances to 

 which the magnetism of our planet is found to be subject. Some of these 

 disturbances are periodic, following the regular courses of the sun and moon. 

 Others are sudden, and are called magnetic storms, but, like the storms of 

 the atmosphere, they have their known seasons of frequency. The last and 

 the most mysterious of these magnetic changes is that secular variation by 

 which the whole character of the earth, as a great magnet, is being slowly 

 modified, while the magnetic poles creep on, from century to century, along 

 their winding track in the polar regions. 



We have thus learned that the interior of the earth is subject to the 

 influences of the heavenly bodies, but that besides this there is a constantly 



