ASTRONOMY AND METEOROLOGY. 399 



opening? in the photosphere, through which the spot appears, are not slop- 

 ing." But according to Wilson's theory the penumbra is formed by the 

 sloping sides of the photosphere and there is the penumbra. Therefore it 

 appears that this explanation does not hold good on V\"iisuu's view. Ac- 

 cording to Sir W. Herschcl another stratum is interposed between the solid 

 body of the sun and the photosphere. On this hypothesis, it is the part we 

 see of the secondary stratum which constitutes the penumbra; if, therefore, 

 it be sensibly depressed below the surface of the photosphere a change of 

 relative position must ensue. ISchwabc's explanation is, that when the phe- 

 nomena in question occur, the secondary stratum has risen to an unusual 

 height, and is not sensibly depressed below the photosphere. 



The address of the President of the Society concludes as follows : 



" You are aware, gentlemen, it has been long known that the intensity of 

 magnetic declination is subject to a daily variation ; and this variation was 

 also known to be in some way connected with the sun, attaining its maxi- 

 mum western limit when that body is at its upper and lower culmination, 

 and its maximum eastern limit about six o'clock in the morning an evening. 

 These arc not the exact times, but they are sufficiently near for our purpose. 

 About the year 1850, Professor Lamont announced that this variation was 

 again liable to r.nothcr variation, which observed a period, from maximum 

 to minimum, and from minimum to maximum, of about ten years. He was 

 led to this result by a discussion of his own observations at Munich. It was 

 shortly after fully confirmed by our colleague, General Sabinc, by the obser- 

 vations made at the Magnetic Observatories of Toronto and Hobarton. But 

 in the course of the latter discussions General Sabinc detected another im- 

 portant circumstance which had escaped Lamont, viz., that the periods of 

 maximum variation of the declination-needle correspond exactly with thoso 

 of the maximum frequency of the solar spots, and vice versa, the minimum 

 of the one with the minimum of the other. Hardly had General Sabine's 

 paper been read before the Royal Society, on March 18, 1852, when intelli- 

 gence was received that two Swiss physicists, 'Professor Gauticr of Geneva, 

 and Professor Wolf of Berne, had arrived at the same conclusion, indepen- 

 dently of each other, from a perusal of Lament's results. 



" All the observations I have mentioned were made during nearly the 

 same time between the years 1840 and 1851 comprehending only a sin- 

 gle period of change. Obviously, therefore, in this state of the inquiry it 

 was of the highest importance to obtain a trustworthy scries made at another 

 time and under different circumstances. Though hardly to be expected, it 

 happened, most fortunately, that such a scries was at hand. 



" The diurnal variation was one of those subjects which, many years ago, 

 had particularly interested the vigorous mini of the lamented Arago ; and 

 among his papers were found the records of a most laborious course of ex- 

 periments, conducted with all the care which no one knew better than he how 

 to bestow on a delicate investigation. These experiments, extending from 

 1820 to 1 S3 1, have been rigorously discussed by M. Thoman, and exhibit 

 the prevalence of the same law that obtains in the later scries. 



" Nor does the evidence of connection rest here. In a recent paper sent to 



