' On the variable Adhn of the Electric Column. 249 



One single circumstance will show that Mr. Ronalds did not - 

 understand my meaning. I could not refer but to the column 

 which I had described, of which an essential circumstance is, 

 that it is in coninmnication with the outside air, and thus in- 

 fluenced by its degree of moisture ; whereas Mr. Ronalds's ex- 

 periments have been made with one of Mr. Singer's columns 

 of 1000 gronpes inclosed in a glass tale: that tuye therefore 

 precluding the action of the exicnal air, the inclosed column 

 cannot be affected by its changini;- degree of moislurt. I do not 

 doubt that, when Mr. Ronalds shall consider tr.at difference be- 

 tween our experiments, he will judge that the results which he 

 relates in his paper, though interesting in themselves, cannot be 

 opposed to mine : but I must come to particulars, because they 

 will contribute to a further explanation of tiiis new physical ap- 

 paratus. 



The action of Mr. Ronalds's column was indicated by the 

 number, in a given time, of the strikings of the gold-leaves in aa 

 electrometer : in his second experiment made under a glass re- 

 ceiver, the strikings having been five in the beginning, while the 

 lajiirometer was 41", and the thermometer 53-}, the strikings 

 were reduced to three, when the hygrometer ascended to 41y,' 

 and the thermometer descended to b'o^ : which experiment ap- 

 pears to favour Mr. Ronalds's idea, that the increase oi moisture 

 rather »lessens than increases the action of the column. But in 

 this experiment the column being inclosed in the glass tube, the 

 increase of 7noisture took place on the surface of tiie latter, wliich 

 produced an increase of conductive faculty for the electric Jiuid 

 on that sm-face, which lessening the difference of electric state of 

 its extremities, diminished consequently its eiTect on the electro- 

 meter. 



The tlrird experiment, iii wlilch the room was gradually heated, 

 sliows a case in which I had jjartly made a mistake, pointed out 

 to me by Mr. Singer. In one of my ex])eriuirnts, when the 

 sun-ra?/s fell on my column, tlie nuinber of strikings sensibly 

 increased, and returned gradually to their former number when 

 the sun-rays ceased to fall on it : this effect I attributed eutirely 

 to tlie action of the sun-rays themselves ; Ijut Mr. Singer con- 

 ceived that it was only the effect of heat thus increased in the 

 column. I considered this explanation as deserving to be sub- 

 mitted to direct experiments ; I have since long observed the 

 column under this point of view, and found that the increase of 

 heat had a great influence to increase the vumber of strikings. 

 I'ut this is not an effect so simple as I thought it at first; for, 

 with the sanic increase of hcnt, I liave found great dirterences in 

 Jhc increase of the cojrespoudeut uumler of strikings ; which 



circum- 



