■ 5*8 Dffcription of a new univiyfal EleByometer, 



The chief experiments which have been made on the force of batteries, by Mr. Brooke*, 

 at Norwich, in the year 1786, and by Dr. Van Marum, in 1785 and 1795. The refults 

 were very different. Some experiments which I made in Holland, and afterwards repeated 

 here, did not feem to confirm either of the two. All that had been done either by Dr. van 

 Marum, or myfelf, was done without the help of fuch an eleflrometer as could indicate 

 the proportional quantities of electric fluid with a fufficient degree of accuracy. 



Mr. Brooke was poffefled of an inftrument of his own invention, with which it was pof- 

 fihle to afcertain the comparative flrength, if managed with the lame dexterity as Mr. Brooke 

 himfelf poffefles. But this inftrument came fo high in price, and was fo very difficult in its 

 ufe, that few eleftricians provided themfelves with it ; which, perhaps, is one reafon, why 

 this fubjeft has fo long remained in obfcurity. I have lately had the good fortune to invent 

 an ele£trometer which has all the properties that fuch experiments require, and is very fira- 

 ple and eafy in its ufe ; and with this I found myfelf enabled to go through fuch experiments 

 as were neceffary, with greater accuracy than any which had been made before. 

 Tlie eledrometer is reprefented in PL xxiii. G H is a long fquare piece of wood, about 1 8 



finches long, and fix inches bi-oad, in which are fixed three glafs fupports, D E F, mounted with 

 brafs balls, a b c. Under the brafs ball a, is a long brafs hook ; the ball c is made of two 

 hemifpheres, the under one being fixed to the brafs mounting, and the upper turned v/ith a 



-groove to Ihut upon it, fo that it can be taken off at pleafure. The ball b has a brafs tube 

 fixed to it, about three inches long, cemented on to the top of F, and the fame ball has a 

 hole at the top, of about one-half inch diameter, correfponding with the infide of the tube. 

 A B is a ftraight brafs wire, with a knife-edged centre in the middle, placed a little below 

 the centre of gravity, and equally balanced with a hollow brafs ball at each end, the centre, 

 or axis, refting upon a proper fhaped piece of brafs fixed in the infide of the ball c ; that fide 

 of the hemifphere towards c is cut open, to permit the end ^ A of the balance to defcend 

 till it touches the ball a, and the upper hemifphere C is alfo cut open to permit the end c B 

 to afcend ; i is a weight, weighing a certain number of grains, and made in the form of a pin 

 with a broad head -, the ball B has two holes, one at the top, and the other at the bottom ; 

 the upper hole is fo wide, as to let the head of the pin pafs through it, but to ftop at the 

 under one, with its fhank hanging freely in ^ ; a number of fuch pins are commonly made 

 to each eleftrometer of different weights 5 ^ is a common Henley's quadrant eledlrometer, 

 and when in ufe, it is fcrewed upon the top of c. 



It is evident from the conftrudlion, that if the foot ftand horizontal, and the ball B be 

 made to touch b, it will remain in that pofition without the help of the weight / ; and if it 



» Though I had read Mr. Brooke's book, as I thoughr, with a fufficient degree of attention when it was 

 firft publilhed, I did not, till lately, obferve that it contained any experiments relating to this fubje6t, till I 

 begun to write this paper, and had occafion to look into his book for fome references. I believe thefc 

 experiments had efcapcd Dr. van Marum's notice likewife, as I never heard him fpeak of them when he was 

 making others of the fame kind. Though Mr. Brooke's experiments were conduced with much fkill and in- 

 telligence, they are fo confufedly arranged, that this had entirely efcapcd my notice ; and I doubt not but 

 that it liad alfo efcapcd the notice of (tvcral other ele£lri(;ians, 



iliould 



