ON THE KEW OBSERVATORY. 



141 



and stronger, and protected from rain, dust, &c. by a cap. This pair of elec- 

 trometers fits into a case and the conductor into a walking-stick. The con- 

 ductor might be jointed and its length increased with great advantage. 



7. Experiments on Frequency of Atmospheric Electricity. 



By these terms is understood the rate at which a new charge rises to its 

 maximum, after a former charge of an atmospheric insulated conductor has 

 been destroyed. 



The old experiments of Beccaria on this property appear to me to have 

 been much less attended to than they should have been. It seems to form a 

 sort of link between natural high-tensioned (frictional) electricity, and gal- 

 vanic, or Voltaic or (Erstedic electricity (electro-magnetism). 



We have as yet merely instituted a few very rough observations of this 

 kind, not having obtained opportunities for prosecuting the inquiry in a 

 satisfactory manner. 



The apparatus employed consists partly of that described at p. 135. The 

 two insulators (a and b) were carefully compared as to insulating power. 

 An arm (of wood, which is not a proper material) projected from the cap of 

 each, outside of the window of the room D (fig. 1), and to these arms were 

 firmly lashed two exactly equal copper conical tube-conductors, carrying 

 small and equal lanterns on their summits. 



After abundant time had been given for these conductors to attain their 

 maxima charges, one only was discharged, and the time which elapsed before 

 that one acquired a new charge equal to the charge of the other is my mea- 

 sure of " frequency." 



May 

 May 



3. 



May 6. 

 May 8. 

 May 9. 



May 16. 



[-Fine clear evening succeeding a fine day. 



/The evening fine and starlight, but some- 

 \ what cloudy. 



The weather dull and overcast. 

 J At 20'» dull and cloudy; at 21" clear and 

 \ starlight. 



/At 21" dull and overcast. The day had 

 I been fine but rather cloudy. 



These few and imperfect observations serve to prove little more than that 

 at different times and under different circumstances (of vveather, &c.) very 

 greed differences in the relations of tension to frequency occur*. Fogs and 

 heavy dews have always great frequency. 



8. Fluvio Electrometer. 

 We are fully convinced that a hard shower of rain, &rc. as frequently robs 

 our conductor of large doses of electricity as that it brings them. 



* The first maximum charges, viz. 10° of these lower rods on the 8th of May at 18" 55"° 

 was greater by one degree than the charge at the same moment of the high conductor on the 

 dome, but after the destruction of the first charge they never rose again to the same height 

 as that of the high conductor by 5 degrees. On the 16th of May, at about 18" 55"", the lower 

 rods at the time of their first charge exhibited a tension equal to that of the high rod, and 

 the maximum charges afterwards were at 20" 55™ 13 degrees lower. These singular facts 

 might possibly be accounted for on principles by which I would explain the experiments of 

 Erman, but shall forbear from theorising here. 



