595 



lehre," written in conjunction \vith his brother, as well as by many 

 other works of his own, but who felt that he was honoured by the 

 privilege of combining his labours with those of so great a master. 

 The units of reference which were chosen by Gauss were the milli- 

 metre in length, the milligramme in weight, and the second in 

 time ; and the horizontal intensity at Gottingen, in terms of these 

 units, was found to be T7625, which gives, assuming a dip of 68 

 1', a total intensity represented by 4*7414. 



It followed, as another consequence of this inquiry, and which may 

 serve to give us a conception of the vast forces with which we have 

 to deal, that the magnetism of the earth might be replaced in exter- 

 nal space by the combined action of 8464 trillions of magnet bars, 

 with parallel axes of the weight of one pouud each ; or, if we 

 should assume the magnetism of the earth to be uniformly distri- 

 buted throughout its substance, the magnetism contained in four cubic 

 feet of its matter would be nearly equivalent to one such magnet. 



The publication of this memoir, a model of the union of experi- 

 mental and theoretical research, produced no ordinary effect upon 

 men of science, particularly in Germany. It was felt that the time 

 had arrived when the same precision which had thus been found to be 

 attainable in the absolute determination of one of the magnetic 

 elements, would not only be equally so in the determination of the 

 others, but also of the changes, whether periodical or occasional, 

 which they were known or suspected to undergo. Were the dis- 

 turbances of the needle, which had been observed to be produced at 

 distant places by the aurora borealis, or other less manifest causes, 

 absolutely simultaneous ; or were they not so ? A magnetical 

 observatory, for the purpose of making the observations which 

 these inquiries suggested, was established at Gottingen, under the 

 superintendence of Gauss and Weber, by whom also instruments 

 were designed which were capable of giving results incomparably 

 more accurate than any which had hitherto been attained. Obser- 

 vatories on the same model were formed in various cities in Ger- 

 many, and ultimately at Greenwich ; the members also of a widely- 

 spread magnetical association engaged themselves to make simul- 

 taneous observations on certain term-days and hours ; and the fine 

 series of magnetical observatories which were subsequently esta- 

 blished at the Cape of Good Hope, Hobarton, Toronto, and elsewhere, 



