174 METEOROLOGICAL PERIODICITY. 



diffused a disagreeable odour, aud the humidity ranged from 57 

 to 68, while in an ordinary fog it is 100. It had a phosjDhore scent 

 appearance, and the light at midnight was compared to that of 

 the full moon. The second instance : — 



The extraordinary fog of 1831 excited public attention in the 



four quarters of the world. It appeared on the 



Coast of Africa August 3. 



At Odessa August 9. 



In South France August 10. 



Paris August 10. 



New York August 15. 



Canton (China) End of August. 



This fog was so thick that it was possible to observe the sun 

 all day with the naked eye, and without a dark glass, and in some 

 places the sun could not be seen till it was 15° or 20° high. At 

 Algiers, United States, and Canton, the sun's disc appeared of an 

 azure blue or of a greenish colour. Where the fog was dense, 

 the smallest print could be read even at midnight. 



M. Arago, the great French astronomer, was at some trouble 

 to prove that these fogs could not be comets, and gave as his 

 principal reason that it would be impossible for the head of the 

 comet to rise and set with the sini for more than a month, which 

 is quite true ; but it is nevertheless possible that the comet left 

 part of his tail with the earth, while the head was too insignifi- 

 cant to be seen. 



I will not stay to point out the bearing of these facts on the 

 opinions previously expressed, for this paper is already too long 

 A wide field for speculation is opened uj) when we look at some 

 of the facts which have been brought forward to-night ; and I 

 think enough has been said to convince us that, in discussing the 

 meteorology of the past or the future, we must ever bear in mind 

 that the solar system is not stationary — it is rolling on into the 

 unknown regions of space. What changes in the cosmical ether, 

 what clouds of meteoric matter, what strange forces we shall 

 encounter in common with other members of the solar system, 

 is yet to be learned. But space is no longer empty : day by day, 

 as science advances, we have to acknowledge new-found denizens 

 of its infinite expanse, and recognise new relations between the 

 earth and the manifold occupants of celestial space which sur- 

 round us. 



Albeit, we know but little yet about those with the presence 

 of which we have been so long familiar. We have yet to learn 

 the functions of electricity in regard to climate ; we have yet to 

 measure how much of it is produced by the friction of millions 

 of meteors rushing through our atmosphere, not to mention 

 numberless other phenomena comparatively within our reach, but 

 which, so far, are by no means within our knowledge. The 



