METEOEOLOGICAL PERIODICITY. 171 



being brought more within our reach, that I think we must look 

 for the causes which produce the proverbial uncertainty of the 

 weather — an uncertainty which will doubtless disappear when we 

 shall have learned more about the smaller elements of the solar 

 system. 



Here also we shall find an explanation of the dependence of 

 the seasons of the two hemispheres, and the reason why a 

 remarkable season in the north may be followed by a similar 

 one in the south, or vice versa. For the causes of which we have 

 been speaking may last days or months, and in the latter case 

 would have a similar effect upon both hemispheres ; but if the 

 duration is short, the similarity in effect would probably not be 

 noticed, for a very clear ether and increased solar effects would 

 have different results in an Australian summer and an English 

 winter. 



In this view of our subject it will be interesting to refer to 

 opinions which have been expressed by others. A well-marked 

 depression in temperature has been observed in Europe in the 

 months of February and May, and the celebrated M. Erman 

 considered that " this is caused by the interposition of meteoric 

 rings between us and the sun, and that the increase in tempera- 

 ture in August and November is caused by their preventing 

 radiation from our globe, and possibly by radiation towards us of 

 a part of the heat which they themselves receive ;" and a "French 

 physicist, M. Deville, who has examined in the most crucial 

 manner the temperatures of the months of August and November 

 since 1808, has detected the fact that in both months there is an 

 increase of temperature about the period of the star showers, 

 and a decrease in February and May, which he does not hesitate 

 to ascribe to the influence of meteoric rings." (Gruilemin, Ast.) 



It may be mentioned that the 10th of August meteor stream, 

 if disposed in the form of a flat ring, would encounter the 

 eclij^tic between the 5th and 11th of February, and would 

 partially eclipse the sun's light. 



As the data upon which these viejvs were founded were for the 

 northern hemisphere, it is interesting to inquire if any similar 

 phenomena have presented themselves here ; and, comparatively 

 short as the time of our observations has been, we get several 

 marked instances, and in every year examined there is a depres- 

 sion in the temperature curve between the 5th and 11th of 

 February, and in nearly all cases it is on the 8th, 9th, or 10th. 



In 18G9 there is a marked fall in the ainiual temperature curve 

 in February, although during February there was less cloud and 

 cool south wind than in March and January. In the tempera- 

 ture curve for that month there is a great depression on the 10th, 

 and on the nights of the 10th and 11th there were terrific cyclonic 

 storms, with thunder and lightning, in v^ydney. 



