390 



of weight 1 milligramme, of time = 1 second mean time). The observations 

 are made with my standard cylinder D (De mutationihus mom€nti,^a,gQ 16, 17) 

 and are reduced to absolute quantity by the method, ibid., page 40, by the 

 constant logarithm, log. A, which, in the calculations, is assumed = 6,00811, 

 instead of 6,00843. 



Christiania, 



Gotheborg, 

 Copenhagen, 



Kiel,'"! . . 

 Bramstedt, . 

 Altona, Kessel's gar- 

 den 



1839, April, 1.5470 

 ... June, 1.5485 

 ... Oct. 1.5422 



1841, April, 1.5464 



1839, Sept. 1.5723 

 ... July, 1.6503 



1840, ... 1.6517 

 1839, Sept. 1.6819 



1.6857 



... July, 1.7120 



Altona, Schumach- 

 er's garden, . 

 Bremen, 

 Hanover, . 

 Magdeburg, 

 Leipzig, 

 Dresden, . 

 Gotba, . , 

 Eisenach, , 

 Cassel, . 

 Gbttingen, 



1839, Sept. 1.7085 



1839, 

 1839, 

 1839, 

 1839, 

 1839, 

 1839, 

 1839, 

 1839, 

 1839, 



July, 

 Sept. 

 Aug. 

 Aug. 

 Ang. 

 Aug. 

 Aug. 

 Aug. 

 Aug. 



1.7172 



1.7490 



1.7662 



1.8092 



1.8252 



1.8057 



1.7973- 



1.7834 



1.7751* 



Taking the horizontal intensity H, in absolute unities for Giittingen 

 = 1.7751, and according to your observations, Gottingen = 0.9783, Dresden 

 = 1-0007, Edinburgh = 0.838 (Paris = 1.000), I find for Edinburgh in ab- 

 solute unities, from the observations — 



In Gottingen H = 1.5205, 

 In Dresden H= 1.5284. Mean 1.5244.5, 

 a little less than in Christiania. When T is the corrected time of 100 vibs. 

 of the Edinburgh cylinder, No. 1, and HT° = A, I find, supposing in Edin- 

 burgh T = 270"578. 



log. A = 5.04769. 

 As the horizontal intensity has so many variations, hourly, daily, monthly, 

 regular and irregular, and undulatory, or perhaps periodical variations in 

 18-19 years, I find the comparison with Paris, especially when it is found- 

 ed upon a single observation, made in dilFerent hours of the day, and after 

 an interval of a month or more, not perfectly sure.t I wiU illustrate this by 

 the following corrected observations of 300 vibrations of my cylinder D here 

 in Christiania, in the garden of the Observatory. 



The greatest difierence between 1841, June 17, 6'' 43' p. m., and 1842, Feb. 

 26, 10'' 32' A. M., is 3"; and between 1841, June 17, and 1842, April 10, 

 5i^ 29' P. M. = 5". 17, imder influence of aurora borealis. 



* The 30th July 1834, Hofrath Gauss observed the same cylinder in the same place in 

 the garden of the Observatory, and found reduced time, T, of 300 vibrations := 759".29, 

 which gives intensity = 1.7672. 



t [The value of the horizontal intensity at Edinburgh compared ivith Paris (.840) was 

 not deduced, as Professor Hansteen supposes, from a single comparison. It was repeated 

 by me in two different years with almost perfect agreement, and confirmed by observations 

 at Brussels, a station independently compared with Paris. Professor Bache of Philadel- 

 phia has since found the same relative intensity for Edinburgh agreeing to the 3d deci- 

 mal place. — J. D. F.] 



