(J4 



times resembling:,' an ill-sbaped arrow-head, at others an 

 irregular trapezium with rounded corners, and that they vary 

 so much in these particulars as to defy every attempt to 

 describe them. 



To try and explain the phenomena, in such a manner that 

 they can be connected with the sun's physical constitution, 

 has been the employment of astronomers since the time of 

 Alexander Wilson in 1774, and the results arrived at are 

 such as to satisfy nearly all the conditions required : — 



1st. There is a dark central mass. 



2nd. There is a luminous stratum, or photosphere, en- 

 closing the former. 



3rd. There is a vaporous envelope in which the two are 

 enshrouded, and which constitutes the real atmosphere of 

 the sun. 



4th. Is an outer chromosphere, lying on the surface of the 

 luminous photosphere, enshrouding the whole, and through 

 which the solar-spots, of various magnitudes, can all be seen 

 during their formation. 



Solar- spots are cavities, or openings of enormous size in the 

 photosphere, and are caused by a down-rush or in-rush of 

 outer vapour into the photosphere — or general plane of con- 

 densation for gaseous matter in the sun — which forms a cavity 

 from 20,000 to 40,000 miles deep. On the 29th of August last 

 I counted 42 of these spots, in three groups, on the surface 

 of the sun while taking a transit, and about the same period 

 there were brilliant displays of Aurora on three consecutive 

 nights. On the 21st September I counted upwards of 70 sun- 

 spots, the whole of which were immersed in the penumbra, 

 and on the same evening appeared a strong Aurora. Sun-spots 

 are now at a maximum, and Aurora disj^lays frequent. 



On the 26th of September, in company with Mr. Eoblin, I 

 counted 43 sun-spots and ;penumbra, and there were auroral 

 displays on the 23rd, 24th, and 25th ; the 26th was cloudy. 



The truth of Galileo's opinion that the solar-spots have 

 some relation to the planets has been verified, first by Schwabe 

 of Dessau, and after by Lamont at Monaco, who individually 

 found that the maximum and minimum of solar-spots, and of 

 the variation of the magnetic needle had each a period of 

 about ten years. 



Contemporaneously with Lamont, General Sabine — who 

 together with Hanstein investigated terrestrial magnetism — 

 from observations made at two opposite parts of the globe 

 (Toronto and Hobart Town), accomplished for the perturba- 

 tion of the magnetic declination, what Lamont had done for 

 the variations was intensity, and proved that a lite period of 

 about ten years was found for both inclination and intensity. 



