NATURAL PHILOSOPHY. 151 



more points, and extending to within about six inches of the bottom, the 

 other extending from the upper side of the cap to an ordinary electrical 

 condenser. 



In experimenting after compressing or exhausting the air within the re- 

 ceiver, the wire reaching to the condenser was disconnected from it. The 

 upper plate was lifted from its place by its glass handle, and its electrical con- 

 dition tested by a gold leaf electrometer. I have found it convenient first to 

 compress the air and close the stop-cock, when the condenser would be 

 found to be charged with positive electricity. Then after discharging all 

 traces of it both from the condenser and the wire leading to it, the air was 

 allowed to escape, and the condenser would become recharged to an equal 

 extent. 



My experiments with this apparatus have extended over about eight 

 months, and I have found the action to bear a strong analogy to that of the 

 electrical machine. In damp or warm weather little or no effect would be 

 produced, whilst at other times, particularly in clear cold weather, the action 

 would be so strong as to diverge the leaves of the electrometer to their 



o o 



utmost extent. In warm weather, when no action would be produced, I 

 have attained the result by cooling the air artificially. A sudden expansion 

 or contraction always increases the effect. 



The results with oxygen gas were similar, but I was not successful with 

 either hydrogen or carbonic acid gases. 



It is believed that the results which have been obtained on a small scale 

 in my experiments may be traced in the great operations of nature. The 

 fluctuations of our atmosphere produce compressions and expansions suffi- 

 cient to cause great electrical disturbances. Particularly should this be ob- 

 served in the dry cold regions of our atmosphere above the effects of mois- 

 ture and vapors ; and it was established by the experiments of Becquerel as 

 well as those of Gay Lussac and Biot that the electricity of the atmosphere 

 increases in strength with the altitude. 



A manifest relation, moreover, between the electricity of the atmosphere 

 and the oscillations of the barometer has frequently been observed. Hum- 

 boldt, treating upon the subject in his Cosmos, remarks among other things 

 that the electricity of the atmosphere, whether considered in the lower or the 

 upper strata of the clouds in its silent problematical diurnal course, or in the 

 explosion of the lightning and thunder of the tempest, appears to stand in a 

 manifold relation to the pressure of the atmosphere and its disturbances. 



The tidal movements of our atmosphere produce regular systematic com- 

 pressions twice in twenty-four hours. These occur with so much regulai'ity 

 within the tropics, as observed by Humboldt, that the time of day is indi- 

 cated within fifteen or twenty minutes by the state of the barometer. And 

 Saussure observed a diurnal change in the electricity of the atmosphere cor- 

 responding with the diurnal changes of the barometer. The electricity of 

 the atmosphere, he observes, has therefore a daily period like the sea, in- 

 creasing and decreasing twice in twenty-four hours. It, generally speaking, 

 reaches its maximum intensity a few hours after sunrise and sunset, and de- 

 scends again to its minimum before the rising and setting of that luminary. 



