61 



As would naturally occur during long-continued northerly 

 and easterly winds, the barometer was high for many months 

 in succession. Mr. Glaisher remarks that the " five months 

 (February to June) were distinguished by having an almost 

 constant atmospheric pressure afeove the average."* It was 

 so also in Bath, and even to the end of July ; this last month, 

 February, March, and June, all having a mean pressure of 

 more than 30 inches. 



To the same cause — the long-continued prevalence 

 of northerly winds — may perhaps be attributed another 

 circumstance, which has been the subject of much remark, 

 the infrequency of thunderstorms during the past summer. 

 Mr. Glaisher observes, f — " It is very remarkable that not- 

 withstanding the continuance of high temperatures, but one 

 thunderstorm occurred at Greenwich during the quarter end- 

 ing 30th of June, viz., on the 29th of May, . . . and 

 generally over the country there have been much less than 

 the usual number of thunderstorms." Mr. Lowe, too, of 

 Nottingham, in his letter to the Times, referred to above,^ 

 states that " there has been much less thunder and lightning 

 than is usually the case during a continuance of hot weather." 

 This, it appears to me, may be explained by the conditions 

 of the atmosphere, however high the temperature, remaining 

 unchanged, so long as the wind keeps steady in the north 

 or north-east, or with only slight oscillations one way or the 

 other. Whenever the wind quits its northerly position for 

 the south-west, and especially in its passage through south- 

 east and south, an intermixture of dry and humid currents, 

 of different temperatures, and probably of different electric 

 conditions, takes place, and a thunderstorm then becomes 

 very probable. It is in summers which, besides being hot, 



* " Reg. Gen. Quart. Report," No. 78, p. 19. 



tid. 



t See b&ck, to p. 46. 



