374 I'lie Philosophical ISociety of Glasgoic. 



posed by my dynamical theory of the solar radiation, the place from 

 which it has been falling, must be either nearer the Sun or more 

 diffused from the plane of Mercury's orbit than we have supposed in 

 the preceding example. With a view to determining whether this 

 theory is tenable or not, it will be necessary to consider whether the 

 appearances presented by the zodiacal light, and the photo-sphere seen 

 round the Sun in total eclipses, allow us to find a place for a sufficient 

 future dynamic supply without supposing a denser distribution of 

 meteors or meteoric vapours than is consistent with what we know of 

 the motion of comets before and after passing very close to the Sun. 



Oil Instruments and Methods for observing Atmospheric Electricity. 

 By Professor Wm. Thomsok. 



After briefly explaining the modes of observation followed by Bec- 

 caria, Yolta, and Delmann, the author proceeded to describe a new 

 method for reducing a conductor to the same electric potential as that 

 of the atmosphere at any point, which had recently occurred to him, 

 and which he had already to a slight extent put in practice, with a 

 good prospect of satisfactory results. The apparatus used for it was 

 shown in action before the Society, as was also a portable electrometer 

 adapted to write with a burning match as collector. The following 

 extracts from a short article written for the forthcoming edition of 

 Nichol's Cyclopaedia contains an account of these methods and instru- 

 ments, as described and exhibited to the Society. The woodcuts repre- 

 senting the instruments are introduced here by the kind permission of 

 the publishers, Messrs. Griffin & Co. 



" A very simple apparatus (Fig. 1), by which I can observe atmospheric 

 electricity in an easy way, consists of an insulated can of water set 

 on a table or window-sill inside, and discharging by a small pipe through 

 a fine nozzle two or three feet from the wall. With only about ten inches 

 head of water, and a discharge so slow as to give no trouble in replenish- 

 ing the can with water, the atmospheric effect is collected so quickly, 

 that any difference of potentials between the insulated conductor and 

 the air, at the place where the stream from the nozzle breaks into drops, 

 is done away with at the rate of five per cent, per half second, or even 

 faster. Hence a very moderate degree of insulation is sensibly as good 

 as perfect, so far as observing the atmospheric effect is concerned. It 

 is easy, by my plan of drying the atmosphere round the insulating 

 stems, by means of pumice stone moistened with sulphuric acid, to insure 



