May 3, 1877] 



NATURE 



\i 



Table I. 



Number of Nnu Groups of Sun-spots observed each Year. The 

 Obseivalions from 1826 to 1S63 7vere made by Ho/rath 

 Schwabe, the others were made at the Kew Observatory. 



From which it appears that 1828, 1837, 1848, i860, and 

 1870 were years of maximum, while 1833, 1S43, 1856, and 

 1867 were years of minimum sun-spot frequency. 



While Schwabe was observing the sun with praise- 

 worthy regularity, Sir E. Sabine was likewise observing 

 the magnetism ol the earth. A freely suspended magnetic 

 needle is usually thought to be very constant as to the 

 direction in which it points, and this is no doubt quite 

 true as far as large fluctuations are concerned. Never- 

 theless, between certain small limits it is always in mo- 

 tion — it has, for instance, a well understood oscillation 

 depending upon the hour of the day, besides which it is 

 also liable to irregular fluctuations that occur abruptly. 

 Now Sabine perceived that these abrupt and spasmodical 

 affections of the needle were most frequent in years when 

 sun-spots were most frequent ; and, furthermore, inas- 

 much as these fluctuations of the magnet are almost in- 

 variably accompanied with displays of the aurora borealis, 

 he came to the conclusion that auroral displays occur 

 moit frequently in years of maximum sun spots. Our 

 readers will no doubt remember the brilliant aurora; of 

 1870, which was likewise (see Table i) a year of maximum 

 sun-spot frequency. 



What we have said refers to the spasmodical affections 

 of the needle, but its diurnal oscillations are not less 

 dependent on the state of the sun's surface. 



Here also we have a maximum amount of fluctuation 

 in years of maximum sun-spot frequency. 



This near relation between sun- spots on the one 

 hand, and magnetic oscillations and auroral displays 

 on the other, is exhibited in Diagram A, which has been 

 compiled by Prof. Loomis, the well-known American 

 meteorologist. 



Close and striking as is the relation between these three 

 associated phenomena exhibited in the above diagram, 

 the mtimacy of this connection m.ay be rendered even 

 more obvious if we confine ourselves to such observations 

 of the solar surface and of magnetic fluctuations as have 

 been made with the greatest possible accuracy. 



For this purpose Schwabe's eye-observations are not 

 precise enough, and we must, as far as sun-spots are con- 

 cerned, make u=e ol some very accurate measurements of 

 the solar spotted area made at liedhill by the late R. C. 

 Carrington, along with the results deduced from the solar 

 photographs taken at the Kew Observatory, under the 

 superintendence of Mr. Warren De La Rue. 



Aain, as far as magnetic observations are concerned, 

 let us employ the results derived from the self-recording 

 magnetographs at the Kew Observatory. 



Furthermore, in order to equalise oscillations of short 

 period, let us plot a solar curve, each point of which re- 

 presents the mean of nine months' sun-spot observations, 

 and alongside of it a magnetic curve, each point of which 

 similarly represents the mean of nine months' magnetic 

 observations. 



A comparison of this kind has been made by the 

 writer of these remarks, the results of which were recently 

 communicated by him to the Royal Society. These 

 results are embodied in Diagram B, in which accurate 

 sun-spot observations are compared with Kew declina- 

 tion ranges, that is to say, with the diurnal oscillations 

 of a magnetic needle, freely suspended at the Kew Obser- 

 vatory. 



A comparison of the two curves given above will show 

 us that almost every prominent fluctuation of the sun- 

 spot curve is represented in the magnetic curve, similar 

 letters being employed to denote what appears to be 

 corresponding fluctuations. 



There is, however, a greater want of similarity for that 

 part of the solar curve which is dotted, but this repre- 

 sents the results of eye-observations taken by Hofrath 

 Schwabe, while the more accurate Kew photoheliograph 

 was unfortunately out of action. 



It will be perceived that the magnetic fluctuations 

 invariably follow after or lag behind the corresponding 

 solar fluctuations in point of time, the mean amount of 

 this lagging being probably six mouths. We may there- 

 fore conclude from these comparisons that there is a very 

 close and intimate relation between the physical condition 

 of the sun's surface and the diurnal oscillations of the 

 magnetic needle freely suspended at the Kew Observa- 

 tory, and also that the former is probably the cause of 

 which the latter is the effect, or at least that the magnetic 

 change lags behind the corresponding solar phenomenon 

 in point of time. Balfour Stewart 



{To be conthnted.) 



THE FRENCH TRANSIT MEDAL 

 XXTE recently announced that the Paris Academy of 

 '' Sciences had presented an appropriate medal to 

 those Frenchmen who were engaged in observing the 

 recent transit of Venus, as well as to all the members of 

 the Academy. By the kindness of the editor of La 



Nature we are able to give an illustration of the principal 

 face of this medal, the design being that of the artist i\l. 

 Alphc'e Dubois. It will be seen that the a tist has had 

 recourse to mythology to represent under a gr iceful form 

 the important astronomical phenomenon. X'enus, in the 



