io ROUGH WAYS MADE SMOOTH. 



really was its constitution, then the theory advanced by one 

 observer of the last eclipse, that at the time of minimum 

 solar disturbance the glowing hydrogen is withdrawn from 

 the corona, would be shown to be incorrect. For 1733 was 

 the actual year of minimum solar disturbance. The pastor 

 of Smoland states that 'during the total obscuration the 

 edge of the moon's disc resembled gilded brass, and the 

 faint ring round it emitted rays in an upward as well as in a 

 downward direction, similar to those seen beneath the sun 

 when a shower of rain is impending.' The mathematical 

 lecturer of the Academy of Charles-stadt, M. Edstrom, 

 observed these rays with special attention : he says that 

 'they plainly maintained the same position, until they 

 vanished along with the ring upon the re-appearance of the 

 sun.' On the other hand, at Lincopia no rays were seen. 

 On the whole it seems clear from the accounts of this 

 eclipse that the inner corona was bright and narrow ; rays 

 issued from the outer faint ring ; but they were very delicate 

 phenomena, easily concealed by atmospheric haze, and thus 

 were not everywhere observed. As rays were seen in July 

 1878, there is nothing in the evidence afforded by the eclipse 

 of 1733, occurring at a time of few spots, which opposes 

 itself definitely to the theory we are considering. But the 

 reddish colour of the corona as already noticed is a doubt- 

 ful feature : in July, 1878, the bright inner corona was of a 

 pearl colour and lustre. 



During the eclipse of February, 1766, the corona pre- 

 sented four luminous expansions, and seems to have pre- 

 sented a greater expansion than we should expect in a year 

 of minimum solar disturbance. Such, however, the year 

 1766 certainly was. The evidence in this case is unfavour- 

 able to our theory not quite decisively so, but strongly. 

 For we should expect that in the year of actual minimum 

 disturbance the corona would be even narrower than in the 

 year 1878, which was the year following that of least distur- 

 bance. And again, a strongly distinctive feature in the co- 

 rona of July, 1878, was the absence of wide expansions, such 



