GAUSS AND WEBER OX TERRESTRIAL MAGNETISM, Z3 



occur contemporaneously, and with almost equal magnitude, 

 over great districts, the means are furnished to divest them al- 

 most entirely of any injurious practical effect. The surv^eyor 

 need only make all his operations with the compass accurately 

 according to time, and cause contemporaneous observ^ations to be 

 made at some other not very distant place ; and it ^^ ill be easy 

 to eUminate the effects of these disturbances by comparison, 

 just as travelling observers render their barometrical determina- 

 tions of height independent of the irregular variations of the 

 barometer, by comparative observations at fixed stations. Of 

 course this has no reference to disturbances of the compass by 

 mineralogical causes. 



The preference given to the Declination over tlie other ele- 

 ments of terrestrial magnetism is less however to be ascribed to 

 these motives than to the present state of our means. The in- 

 vestigation of the laws of nature has for the philosopher its own 

 value and its own reward ; and a peculiar charm suiTounds the 

 recognition of measure and harmony in that which at first 

 sight appears wholly irregular. In following the constantly 

 varying changes of the Declination, the apparatus at present 

 employed leaves, as to certainty and precision, nothing more to 

 wish ; but the same cannot be said of the present means of ob- 

 servation of the other two elements. The time is therefore not 

 yet come for including the latter in the cii-cle of combined in- 

 quiry ; as soon, however, as the means of observation shall be 

 so far perfected, that we can recognise with certainty, follow 

 with ease, and measure with accuracy, the variations, and chiefly 

 the rapidly varying changes, in the other t^\ o elements of ter- 

 restrial magnetism, these variations will have the same claims 

 on the united activity of natural inquirers as the variations of 

 the declination now possess. We venture to hope that this day 

 is not far distant. Gauss. 



I. 



Remarks on the Arrangement of Magnetical Observatories, and 

 Description of the Instruments to be placed in them. 



The instruments with which the observations were made, which 

 are to be mentioned in these pages, differ in many respects from 

 all previously employed, and a more accurate knowledge of their 

 construction is indispensable, in order to judge of the results 



