GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 83 



Finally, from this value of r, and from that of t, determined by 

 observation, may be deduced the value : 



1 1 5-0641 



t^Jr 6-67 • ^/ 8765000 10* 



This number suffices for the comparison of all intensities mea- 

 sured with the same instrument, however the magnetic condition 

 of the apparatus may have varied. 



Further, the number T, which expresses in absolute measure 

 the resulting intensity of the earth's magnetism, may be ascer- 

 tained by deducing from the obsen-ations the value of C, and 

 multiplying the former number by its square root. C is calcu- 

 lated from the obseiwed values ofe, h, andj:;, the mass of the mil- 

 ligramme being taken as the unity of mass : 



C = 9-8696+ ^^^ "^p^^'^^ + 142000 = 0-12272 + 10'" 



whence T is deduced 



T = 5-0641 . 'v/O-12272 = 1*774. 



5. Examination of the result. 

 This number 1*774, expressing the intensity of terrestrial 

 magnetism on the 18th of January, 1837, possesses, as an 

 absolute measure, the advantage of being directly comparable 

 with the results obtained in 1834 with the magnetometer of 

 the Gottingen magnetic obser\'atory, published in the Gottingen 

 gelehrten Anzeiyen of that year. They will be found in part 

 128, (with the account of the newly-constructed building, and 

 of the insti-uments, as well as of the first experiments performed 

 there). They are as foUow : 



July 17 1-7743 



— 20 1-7740 



— 21 1*7761 



Two apparatus destined for the same purpose can hardly be 

 more dissimilar than the small apparatus above described, and 

 the magnetometer. It results from the comparison, that the 

 intensity of the terrestrial magnetism in Gottingen has under- 

 gone hardly any alteration from 1834 to 1837. 



We have also a direct comparison of this number obtained 

 for Gottingen with the result of observations with a third ap- 

 paratus, differing widely from both the others made at Munich, 

 April 1st, 1836, viz. 1*905, and with the number found for 



f2 



