140 COSMOS. 



minimum between 1843 and 1844, and its maximum from 

 1848 to 1849. After the decimation has thus increased for 5 

 years it again diminishes for a period of equal length, as is 

 proved by a series of exact horary observations, which go back 

 as far as to a maximum in 1786^-. 7 * In order to discover a 

 general cause for such a periodicity in all three elements of 

 telluric magnetism, we are disposed to refer it to cosmical 

 influences. Such a connection is indeed appreciable, accord- 

 ing to Sabine's conjecture, in the alterations which take place 

 in the photosphere, that is to say, in the luminous gaseous 

 envelopes of the dark body of the sun. 80 According to the 

 investigations which were made throughout a long series of 

 years by Schwabe, the period of the greatest and smallest 

 frequency of the solar spots entirely coincides with that 

 which has been discovered in magnetic variations. Sabine 

 first drew attention to this coincidence in a memoir which 

 he laid before the Royal Society of London, in March, 1852. 

 " There can be no doubt," says Schwabe, in the remarks 

 with which he has enriched the astronomical portion of the 

 present work, "that, at least from the year 1826 to 1850, 

 there has been a recurring period of about 10 years in the 

 appearance of the sun's spots, whose maxima fell in the 

 years 1828, 1837, and 1848, and the minima in the years 

 1833 and 1843." 81 The important influence exerted by the 

 sun's body, as a mass, upon terrestrial magnetism is confirmed 

 by Sabine in the ingenious observation, that the period at 

 which the intensity of the magnetic force is greatest, and the 

 direction of the needle most near to the vertical line, falls, 

 in both hemispheres, between the months of October and 



the same length of time; on which account the winter motion (the 

 amplitude of declination) is always twice as small as the summer motion 

 (see Lament, Jahresbericht der Sternwarte zu Milnchenfur 1852, s. 54 

 60). The Director of the Observatory at Berne, Rudolph Wolf, finds 

 "by a much more comprehensive series of operations, that the period of 

 magnetic declination which coincides with the frequency of the solar 

 spots, must be estimated at 11.1 years. 



7 9 See page 75. 



80 Sabine, in the Phil. Transact, for 1852, pt. i, pp. 103, 121. See 

 the observations made in July, 1852, by Rudolph Wolf, above reierred 

 to in page 76 of the present volume ; also the very similar conjectures 

 of Qautier, which were published very nearly at the same time in the 

 BibliotMque l/niverselle de GenZve, t. xx, p. 189. 



81 Cosmos, vol. iv, p. 397- 400. 



