124 The Climate of Great Britain. 



true averages, and taking a curved line (the curve of Fig. 3, 

 in fact) in such a way as to take off the most marked irregu- 

 larities of the true curve of averages ; or, to use the words of 

 the meteorologist who constructed the Greenwich table of 

 means, Mr. Glaisher, a curved line was drawn which 

 passed through or near all the points determining the true 

 curve of averages, " and in such a way that the area of the 

 space above the adopted line of mean temperature was equal to 

 that below the line." Despite this process, the curve exhibits 

 no less than fourteen distinctly marked maxima of elevation, 

 and a much larger number of variations of flexure. The 

 sudden variations of temperature at the beginning of February, 

 early in April, and early in May are very remarkable ; they 

 have their counterparts in the three variations which take 

 place between the latter part of November and the end of the 

 year, only these occur in much more rapid succession. The 

 nature of the curve between June and August is also remark- 

 able, as are the three convexities which are exhibited in the 

 September, October, and November portions of the curve. 



If we follow our leading meteorologists in taking the curve 

 of Fig. 3 as representing the true annual climate of London, 

 how are we to assign physical causes for the remarkable varia- 

 tions above indicated ? Not easily, I take it. It were, indeed, 

 as easy as inviting to speculate on cosmical causes ; — to follow 

 Ertel, for instance, in assigning effects to those zones of 

 meteorites which are known to intersect the earth's orbit, and 

 others which may fairly be assumed to fall within or without 

 that orbit. It may be, perhaps, that the fifty-two recognized 

 shooting-star periods have, some of them, their counterparts 

 in heat-changes ; but certainly the time has not yet come to 

 pronounce a consistent theory of such effects. The evidence 

 afforded by the Greenwich curve on this point is unsatisfactory 

 to say the least. The elevation at the beginning of January, 

 and the marked irregularity in February, correspond to ErtePs 

 views ; so also the fact that large aerolites have frequently 

 fallen in the first week in April, about the 20th of April, about 

 the 18th of May, early in August,* about the 19th of October, 

 and early in December, seems to correspond to elevations in 

 the curve ; while the depression opposite the 12th of May, 

 might be referred to the intervention of the zone of meteors, 

 which causes the now celebrated November shower. But, the 

 negative evidence is almost equally strong. Where, for in- 

 stance, is the elevation which one would expect, on Ertel's 

 theory, in November? Also,, if the cause of the observed 

 irregularities were that suggested by Ertel, the curves for other 



* Reference is not made here to the August shodting-star shower, which takes 

 place a week later than the epoch alluded to. 



