GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 65 



were made, not according to the time of the place, but simulta- 

 neous with those of Gottingen, the comparison of the single days 

 would afford an opportunity for other combinations, \vhich, when 

 continued through a considerable time, would possess great in- 

 terest. Observers who follow this plan, i. e., of making the 

 times of observation simultaneous with ours, are requested to 

 communicate the daily observations ; this may be done in divi- 

 sions of the scale, provided the necessary elements of reduction 

 are at the same time communicated. Gauss. 



IV. 



Description of a small portable Apparatus for measuring the ab- 

 solute intensity of Terrestrial Magnetism. 



Among the numerous applications of the magnetometer, the 

 most important is that of measuring the absolute intensity of 

 the earth^s magnetic force, as described in the memoir entitled, 

 Intensitas vis magneticcB terrestris ad mensuram absolutam revo- 

 cata ; Auctore Carolo Friderico Gauss '. Gottingen, 1833. Fre- 

 quent mention will be made in the com'se of this work of this 

 application of the magnetometer, which enables us to compare 

 numerically with one another the results of experiments made in 

 the most distant parts of the globe, at different epochs, and with 

 apparatus not previously compared. Everything necessary to be 

 known for these experiments, as well as everything that may 

 sei've to facilitate them, will be communicated from time to time. 

 Results of such absolute measurements will also be noticed, and 

 their value shown in estabUshing, on a scientific basis, the sci- 

 ence of galvanism. 



These important absolute measurements can be performed 

 with the accvu'acy they deserve only with the magnetometer, 

 and, indeed, only in a completely furnished observatory. Few 

 such obsei*vatories, however, exist at present, and few philoso- 

 phers, therefore, have these means at their disposal ; while there 

 are many who take an interest in the results, and desire to be 

 enabled to form such an opinion concerning them as can hardly 

 be satisfactorily obtained \Aithout actually taking pai't in the 

 observations and calculations, even though less minute and ac- 

 curate. The simple means which it is the object of this chapter 

 to describe may be procured by every person. The description 

 and mode of employing them are with the more propriety given 



VOL. II. part v. e 



