1864.] 



Prof. Erman — Magnetic Elements at Berlin, 



223 



meters of ^ have not yet been perfectly exposed, I preferred in the pre- 

 sent to treat the latter as mere functions of m and x» In the following 

 Table of employed mean declinations for the moments t, to each of them 

 is subjoined the value of by whose subtraction it has resulted from the 

 momentary value furnished by observation. This arrangement will allow 

 us to appreciate (and, if wanted, to correct for) the influence exerted by 

 any periodical variation of ^ upon the final result of my observations. 

 It may, too, be convenient to observe that for some of the following west 

 dechnations (D), as well as for the before-mentioned intensities (T) and in- 

 clinations (I), the observations were made in latitude p — Ap, and longitude 

 l — (where j9 and I mark the corresponding and above alleged values for 

 my ordinary place), and that then the directly obtained results, viz. J— Atf, 

 T— AT, or 2— Af, have been reduced by 



Ad/= — 0-0940 . Ai)-0-6103 . A?; 



AT=-07480. 10-3.AP + 0-2152. 10-3. A?; 



Af= + 07405 . Ai)-0-1861 . AZ ; 

 the minute of arc being the unity for A^, Ac?, Az, and A?. 



These equations, which result from the Gaussian constants with the given 

 p and I, are sufficiently approximated when, as with us, Ap and A^ do 

 not exceed a few minutes. So then were obtained : 







Mean declination. 





Momentaiy 







Date of 



decliaation. 



d. 



observation. 

 1800+^. 



Mean 







declination, 

 0. 



observation. 



Calculated. 



1731-60 







12 1805 



12° 19-85 



1784-00 







17 59-65 



17 46-09 



1805-40 







18 1-35 



18 7-86 



1819-00 







17 36-50 



17 48-06 



1825-79 



-1-80 



17 24-46 



17 28-37 



1828-33 



-4-08 



17 21 -35 



17 19-34 



1834-05 



-1-24 



17 2-69 



16 55-65 



*1849-62 



+2-74 



15 21-55 



15 24-39 



*1850-63 



+2-96 



15 20-48 



15 20-47 



1853-81 



+4-32 



14 55-17 



14 58-26 



1854-36 



-2-86 



15 1-05 



14 54-19 



1856-58 



+ 1-13 



14 38-13 



14 37-40 



1857-49 



-5-95 



14 33-88 



14 30-29 



1858-54 



-5-61 



14 21-15 



14 21-96 



1859-58 



-4-87 



14 14-24 



14 13-59 



1861-50 



+4-47 



13 53-70 



13 57-63 



1862-55 



+0-12 



13 49-83 



13 48-72 



1863-79 



+4-48 



13 36-85 



13 37-99 



A fourth of the weight of each of the other observed values being given 

 to each of the two marked *, the whole is best represented by 



i?=18°8'-46 + 0'-26S20 ^~0'•070665 ^^ . . . (IV). 



