On the Electric Column of Mr. De Luc. 467 



that in choosing the term Electrico-galvanic agency, your view 

 of a suljject (containing so many contrary opinions) is fonnderl 

 upon a far more extensive knowledge of it than I can pretend 

 to. Mr. De Luc remarks that the instrument is not tol)e called 

 electrico-galvanic, but electric column as he has named it, ''since 

 there are no galvanic and only electric effects." The reason of 

 my concurrence with him in the use of the terms electric column 

 and elecl.ric agency is, because I think his ingenious experiments 

 and forcible deductions, and their subsequent confirmation by 

 the experiments of Sig. Zamboni and others, go far to prove the 

 truth of the proposition which Mr. De Luc here advances. At all 

 events, he has started game which may afford good sport ; and 

 it no doubt will do, so if it is pursued with the indefatigable ar- 

 dour which he has so eminently exhil)ited in his several valuable 

 writings and successful labours. 

 I remain, sir. 



Your much obliged and humble servant. 

 Hammersmith, .Tune 6, 1815. FrANCIS RoNALDS. 



Jittaclicd ii fine platina wire as a girtli round my cork-ball, and found that 

 its indications then agreed with those of the other pendulums and needles; 

 but have now procured from my good friend Mr. Teid a ball of silk with a 

 very fine platina girth, so light that it weighs but little more than the cork. 



I presume it has been shown, that the frequency or quantity of the elec- 

 tricity of the column at differcut intervals does not always bear a constant 

 ratio to its intensity; and therefore, that any apparatus where a pendulum 

 in constant limited oscillation is used, cannot measure both these powers. 

 Even the frequency with which the leaves of Mr. Bennett's electrometer 

 open and strike the sides for a certain nunil)er of seconds, does not be- 

 come a comparative measure of the power of the column .it different times, 

 if this expression is used in a general sense. 



I have a small column to which is attached a large electrometer for 

 measuring by the divergence of the leaves its intensity, and to which I 

 sometimes attach a smaller electrometer for measuring its frequency by the 

 striking of the leaves. This apparatus proves the fact very clearly; for 

 sometimes, when the large one indicates a certain intensity, the small one 

 by being applied to the <;olumn will strike its sides much more frequently 

 than at others, although the divergence of the large one remains the same, 

 or has even diminished. Sometimes the intensity and frequency will go on to 

 increase together in corresponding ratios to a certain maximum, and then 

 alter. At other times the former will stop, and the latter go on to increase. 

 These phanomena depend, I believe, principally upon the variation in the 

 hygrometric state of the disks of paper. The influence of moisture to in- 

 crease the general power of the column to a certain extent Mr. Dc Luc 

 first observed. On columns inclosed in glass tubes it of course cannot act 

 so powerfully; and moisture, by being deposited on the glass, may, as Mr. 

 Ilouldy has shown, diminish its power by injuring the insulation. But, by 

 subjecting a column to the action of a moist and a drier atmosplierc whilst 

 its supports were not so circumstanced, I think I have proved that, in th» 

 u^ual hygrometric state of the air, the stale of insulation has little or no 

 j-hnre in tlie above phxnomena. 



Gg2 VLXXXin. No- 



