lioyal Society, 299 



For unities, the millimetre, the milligramme, and the second in time 

 have been adopted. The manner in which the measurement of the in- 

 tensity has been determined by them cannot here be specified : the 

 numbers, however, remain the same, provided the unity of space, and 

 that of weight ( properly speaking, unity of masses) , are changed in the 

 .same proportion. These experiments vary partly with regard to the 

 greater or less degree of care with which they were conducted, partly 

 with regard to the places in which they were made, and to the needles 

 employed. 



The experiments VII, VIII, IX, were in every respect performed 

 with all the precision which the apparatus in the present state admits 

 of, and the distances were measured with microscopic exactness. In 

 experiments IV, V, VI, X, some operations have been performed 

 with rather less care j and the first three experiments are still less 

 perfect in this respect. 



The needles employed in the first eight experiments were not in- 

 deed the same, but they were nearly alike in size and weight (the 

 latter between 400 and 440 grammes) ; the principal needle in ex- 

 periment X. weighs 1062 grammes j experiment IX. on the other 

 hand was made, with a much smaller needle (weight 55 grammes), 

 merely for the sake of ascertaining the degree of precision, which, all 

 other precautionary means being alike, may be attained in using a 

 needle of such small dimensions : the result of this experiment is 

 therefore much less to be depended upon. 



Experiments VII. to X. were made in one and the same place in 

 the observatory j the preceding ones in other places in the same ob- 

 servatory, and in apartments of the author's dwelling-house. No per- 

 fectly pure results therefore could be derived from these latter expe- 

 riments, inasmuch as the iron in those localities, and particularly in 

 the observatory, becoming itself magnetic by the magnetism of the 

 earth, would necessarily react upon the needle, and confound its in- 

 fluence with that of the terrestrial magnetism. Such places, indeed, 

 were uniformly chosen in which neither fixed nor moveable masses 

 of iron were near ; nevertheless, even the more distant ones may 

 not have been altogether without their effect upon the operations. 

 However, on casting a look over the different results, it appears pro- 

 bable, that in no one of those localities, the modification of the ter- 

 restrial magnetism produced by extraneous influence exceeds the 

 hundredth part of the whole. But results commensurate to the pre- 

 cision belonging to this mode can only be expected in a locality en- 

 tirely free from the influence of iron. 



In order to obtain the intensity of the whole force of the terrestrial 

 magnetism, the numbers found are to be multiplied by the secant of 

 the inclination. Mr. Gauss intends at a future period also to treat this 

 element according to peculiar methods -, in the mean time he merely 

 mentions that on June the 23rd he has found 68° 22' 52" with the 

 inclinatorium of the University collection of instruments, — a result 

 which, as the observation was made in the observatory, and therefore 

 not without the reach of local interference, may possibly require to 

 be rectified by other observations 



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