VOL. XLIV.] PHILOSOPHICAL TKANSACTIONS. 215 



A Letter from to Mr. John Ellicol, F. R. S. of weighing the Strength of 



Electrical Effluvia. N° 479, p. 96. 



, Having heard that Mr. Gray gave an account of balls caused to move round 

 each other by means of electrical effluvia, I was very desirous of seeing so delight- 

 ful a sight. And though I was disappointed in my expectation of a circular mo- 

 tion, yet I found it easy to make two balls act on each other, in a very entertain- 

 ing manner, for a long time; and that with such a constancy and regularity, as 

 to the effect, that I apprehend we may thence deduce a gauge or standard for 

 measuring electrical powers, and comparing the quantities and strength of the 

 virtue infused into, or remaining in non-electrical bodies, after given times, &c. 



This, with a great desire to be able to estimate and compare the effects of 

 experiments with some certainty, and to do something more than amuse myself 

 and friends with the several surprising phenomena which those experiments pro- 

 duce, led me to think, of a method, which seems to be quite new, and to pro- 

 mise fair to afford much new light. It is to try or weigh the strength of the 

 electrical effluvia, virtue, or power, by causing it to act on a balance. 



I found, the first day, that this method answered even beyond expectation ; so 

 that several non-electrical balls, placed successively underneath one of the scales, 

 and then imbued with electrical virtue in the common way, would presently cause 

 that scale to descend 1, 3, 4, or 5 inches, and seem to cleave, for 10 seconds or 

 more, to the several bodies so placed underneath, some having much greater 

 effect than others. Whence it appeared, that there was a sufficient latitude for 

 comparing very different forces, if any such there were. At the next and only 

 opportunity I have had since, I used flat instead of globular bodies; and then I 

 found the effects far more considerable ; some of them, whose upper surface was 

 about 3 inches square, having attracted and held down one scale, when there 

 were about 200 grains weight in the other. 



Though I am tempted to communicate some things, already observed by this 

 means, with much delight, I reserve them at present for a further examination. 

 Note, that the strings of that scale which is to be acted on, must be long, and 

 non-electrical, and thick; that there may be a ready passage for the electrical 

 virtue to run off, as fast as it is received. Instead of a brass scale-pan, I used a 

 flat piece of cork, filed very smooth and even, especially on the under surface. 

 The other scale needs no alteration, provided the strings be made of silk, as usual, 

 and short enough to keep that scale out of the reach of the electric virtue, which 

 is to act on the former. If the beam were 3 or 4 feet long, the strings of both 

 scales might be of a length, which would make it less troublesome to put in 

 and take out weights. 



