Royal Society, 409 



Thunder frequently follows a considerable duration of 

 dry hot weather, both these circumstances being favour- 

 able to the collection and insulation of electric matter. 



The extraordinary elevation of the barometer which 

 sometimes happens, is said to arise from two currents of 

 air, from opposite directions, meeting and accumulating 

 over a particular spot ; and the extraordinary depression of 

 the barometer* from the circumstance of two currents of 

 air setting out from any particular spot: in either case a 

 commotion of the air is necessarily produced, whilst the 

 equilibrium is restoring. 



That the atmosphere, as well as the sea, is affected pe- 

 riodically in a small decree by the attraction of the moon, 

 is well ascertained ; but it does not appear that the wea- 

 ther is in the least influenced by any mechanical effect of 

 the moon. 



I was first led to the remark noticed in a former paper, 

 respecting the difference of the weather during the increase 

 and during the waneoi the moon, by observing that eclipses 

 of the moon were much seldomer obscured by a clouded 

 atmosphere than eclipses of the sun ; and subsequent ob- 

 servations of a general nature have somewhat confirmed 

 me in the same opinion. 



P. S. I omitted to mention, in my paperou the measure- 

 ments of heights by the barometer, (Phil. Mag. for Oct. 

 1610, p. ^ 7 8) that when the lower station in the barometer 

 is behw what is provided for in Table 2, p". 2*9, as is some- 

 times the case in different gradations of heights, the most 

 accurate method will be, first to calculate the whble height, 

 assuming 30 inches of the barometer for the lower station ; 

 dnd in like manner calculate the lower portion only, and 

 then subtract the latter product from the former. 



Oxford, Dec 15, 18 1Q. R D . WALKER. 



LXXXIII. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



\Jn Dec. 6th, the reading of Mr. Davy's Bakerian Lecture 

 was continued, and on the 13th concluded. In this part 

 of the lecture Mr. Davy detailed a number of experiments, 

 which he regarded as showing that when any metallic 

 oxide is converted into the substance improperly called a 

 muriate, but which is a binary combination or oxymunatic 

 gas and a metal, the oxygen produced is exactly that which 

 2 G 3 had 



