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foot, which was the greatest length of wire ever melted. We have no account of this experiment having been afterwards repeated on a scale of any considerable magnitude till the year 1785, when I constructed a battery for the Teylerian Society, at Haerlem, containing 135 square feet of coated surface. With this battery 180 inches of the same sort of wire was melted, which seemed to be much more than in proportion to the size of the battery, as this was about 1.3 inches for each square foot. This battery was afterwards increased to 225 square feet of coating, and with this 300 inches of the same sort of wire melted, which was also at the rate of 1.3 inches for each square foot. Some time after this, I made another battery for the same society, containing 550 square feet of coating, composed of 100 jars of 5 square feet each. The same sort of wire was not tried with this; but it could be calculated from other sorts of wire which it melted, that it was capable of melting 655 inches, being also at the rate of 1.3 inch for each square foot. This increase of power, which is almost double that of Mr. Nairne's, might be attributed to the acting power of the machine; for though Mr. Nairne's machine possessed the strongest acting power of any machine made at that time, yet it could not be supposed to possess the high charging property of the Haerlem machine.

Since my return to London I have made several batteries, commonly composed of fifteen jars, each containing 168 square inches of coated surface, consequently the whole battery contains seventeen square feet of coating. This battery, according to the proportion of that made by Mr. Nairne, should fuse 6.3 inches, and in proportion to the Haerlem batteries, it ought to fuse twenty-two inches; but instead of following that proportion, it is found to fuse sixty inches, which is an astonishing increase of force. For the battery is only about one-third part of that of Mr. Nairne, and fuses a much greater length of wire; and though it is only part of that at Haerlem, yet it fuses of the length of wire. It seems difficult at first sight to account for this advantage. I have before remarked that the proportional difference between the charge of the battery at Haerlem and Mr. Nairne's, might be accounted for from the high charging power of the great machine; but the result of the last-mentioned experiments overturns that notion, as it can by no means be supposed, that a single two-feet plate machine, which I have used to charge the battery of seventeen feet so high as to fuse sixty inches, can have a higher charging power than that at Haerlem; so that it must proceed from some other cause. It might be questioned whether all the batteries were alike judiciously constructed. As to Mr. Nairne's, it certainly had faults, both with respect to the coating and the mounting of the jars; but the batteries at Haerlem were as judiciously constructed as my present one which I am speaking of, and which exceeds them in such an astonishing degree in its proportional force. The only difference between my present batteries and those at Haerlem is in the glass. They were

composed of glass blown in Bohemia, and those which I make here are of white flint glass. I mention this fact, but I am not inclined to think that the cause of the difference depends on the glass, because I remember to have melted the same quantity of wire with one jar of that kind of glass when in Amsterdam, as I do at present with white flint glass; so that it only remains now to be sought for in the manner of using or charging each battery, and here we shall probably find a means of solving this paradox.

With regard to the batteries at Haerlem, they were never attempted to be charged but in dry weather, being such as was then commonly called favourable for electrical experiments. There was no convenience in the room where the machine and batteries were used for making a fire, which was therefore ill calculated for electrical experiments: the batteries previous to charging, were made as clean and dry as possible; and if they received a charge so high as to cause a spontaneous explosion, they were then looked upon to be in their most favourable state.

It was about this time that we were told by Mr. Brooke, that a coated jar would take a higher charge when dirty, than when clean; but the degree of dirtyness was so ill defined, that I must own I never could dirty a single jar so as to answer, or to come near what was said of it; and to pretend to bring all the jars in a large battery, containing upwards of two hundred, into that state of dirtyness was never attempted; neither does it appear that Mr. Brooke ever thought of dirtying his battery jars, as he only mentions trying two small bottles, whose charging property was very differently increased by his method of dirtying.

Some time afterwards, in the year, 1792, I happened casually to discover that a coated jar, when it was a little dampish in the inside above the coating (which is always the case when a jar is fresh coated), would take a higher charge than it would do after it had been coated for some time, and was quite dry in the inside; and also, if the atmosphere was in a moist state, and the jar not dryed in the inside, it would take an equally high charge. From this it appeared evident to me, that if I could, by any means, render the inside of the jars damp, it would answer the same purpose. Breathing into a jar was tried, and the success was such, that it would receive and retain nearly double the quantity of electric fluid it could retain when dry; and in trying to fuse wires with the charge of one jar in a dry state, no more than five inches could be fused, though after breathing into it, twelve inches were fused.

This method appeared at first sight to have increased the force to more than double; but notwithstanding so evident and striking an effect, I did not think of trying what would be the result of charging a battery, after the jars had been breathed into; being deterred, as I suppose, from the idea of its being so contradictory to the common method of using batteries, which was never attempted to be done but when the atmosphere was in a tolerably dry state,

and the jars previously cleaned. But in March, 1796, being engaged in a course of experiments, when the atmosphere was so very dry that a spontaneous discharge always took place before I had a sufficient force to answer my purpose, it then occurred to me to try what the effect of breathing into the jars of the battery would be. In this trial, or research, it became necessary first to ascertain the real charge which the battery was capable of receiving before a voluntary explosion took place. The battery contained seventeen square feet of coated glass, and was composed of fifteen jars: it was found in the then state of the atmosphere to be incabable of fusing a greater length of wire than eighteen inches. But after breathing into each jar through a glass tube, it took a charge which fused sixty inches, to my very great surprise and satisfaction, as I then thought I had obtained a method of making one battery perform the functions of three; because three times the quantity of wire was fused, as appears by comparing this with what had been performed by increasing the surface of batteries by former electricians. This notion seemed to be justified, by observing in Dr. Van Marum's works, that I had enlarged his batteries at three different times; his first contained 135 square feet coating, the second 225 square feet, and the third 550; and the highest charge of the first was just sufficient to fuse 180 inches of iron wire of of an inch diameter, or six inches of iron wire of an inch diameter; the highest charge of the second fused 300 inches of the first-mentioned wire, or ten inches of the last-mentioned; the highest charge of the third fused twenty-five inches. We find that these batteries increased in power in the same proportion as the coated surface was increased. I was present when the wire was fused by the two first-mentioned batteries, but at the third not; however we have no reason to doubt Dr. Van Marum's report. These experiments supported me in my first notion, that I had discovered a new method of increasing the force of a battery to three times its usual power; but being unable to account for it to my own satisfaction, I resolved to make a course of experiments in order to throw some light on the subject.

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The chief experiments which have been made on the force of batteries were by Mr. Brooke,* at Norwich, in the year 1786, and by Dr. Van Marum, in 1785 and 1795. The results were very different. Some experiments which I made in Holland, and afterwards repeated here, did not seem to confirm either of the two. All that

Though I had read Mr. Brooke's book, as I thought, with a sufficient degree of attention when it was first published, I did not till lately observe that it contained any experiments relating to this subject, till I begun to write this paper and had occasion to look into his book for some references. I believe these experiments had escaped Dr. Van Marum's notice likewise, as I never heard him speak of them when he was making others of the same kind. Though Mr. Brooke's experiments were conducted with much skill and intelligence, they are so confusedly arranged, that this had entirely escaped my notice; and I doubt not but that it had also escaped the notice of several other electricians.

had been done either by Dr. Van Marum, or myself, was done with-out the help of such an electrometer as could indicate the proportional quantities of electric fluid with a sufficient degree of accuracy.

Mr. Brooke was possessed of an instrument of his own invention, with which it was possible to ascertain the comparative strength, if managed with the same dexterity as Mr. Brooke himself possesses. But this instrument came so high in price, and was so very difficult in its use, that few electricians provided themselves with it; which, perhaps, is one reason why this subject has so long remained in obscurity. I have lately had the good fortune to invent an electrometer which has all the properties that such experiments require, and is very simple and easy in its use; and with this I found myself enabled to go through such experiments as were necessary, with greater accuracy than any which had been made before.

The electrometer is represented in Plate II. G H is a long square piece of wood, about eighteen inches long, and six inches broad, in which are fixed three glass supports, D E F, mounted with brass balls, a b c. Under the brass ball a, is a long brass hook; the ball c is made of two hemispheres, the under one being fixed to the brass mounting, and the upper turned with a groove to shut upon it, so that it can be taken off at pleasure. The ball b has a brass tube fixed to it, about three inches long, cemented on to the top of F, and the same ball has a hole at the top, of about one-half inch diameter, corresponding with the inside of the tube. A B is a straight brass wire, with a knife-edged centre in the middle, placed a little below the centre of gravity, and equally balanced with a hollow brass ball at each end; the centre, or axis, resting upon a proper shaped piece of brass fixed in the inside of the ball c; that side of the hemisphere towards e is cut open, to permit the end c A of the balance to descend till it touches the ball a, and the upper hemisphere c is cut open to permit the end c в to ascend; i is a weight, weighing a certain number of grains, and made in the form of a pin with a broad head; the ball в has two holes, one at the top and the the other at the bottom; the upper hole is so wide, as to let the head of the pin pass through it, but to stop at the under one, with its shank hanging freely in b; a number of such pins are commonly made to each electrometer of different weights; k is a common Henley's quadrant electrometer, and when in use it is screwed upon the top of c.

It is evident from the construction, that if the foot stand horizontal, and the ball в be made to touch b, it will remain in that position without the help of the weight i; if it should by any means receive a very low charge of electric fluid, the two balls b, B, will repel each other; B will begin to ascend, and on account of the centre of gravity being above the centre of motion, the ascension will continue till A rests upon a. If the balance be set again horizontal, and a pin i, of any small weight, be put into its place in B, it will cause B to rest upon b, with a pressure equal to that weight,

so that more electric fluid must be communicated than before, before the balls will separate; and as the weight in в is increased or diminished, a greater or less quantity of electric fluid will be required to effect a separation.

When this instrument is to be applied to a jar, or battery, for which purpose it was invented, one end of a wire, L, must be inserted into a hole in b, and the other end into a hole of any ball proceeding from the inside of a battery as м:* k must be screwed upon c, with the index towards A; the reason of this instrument being added, is to shew, by the index continuing to rise, that the charge in the battery is increasing, because the other part of the instrument does not act till the battery has received the required charge.

If this instrument be examined with attention, it will be found to consist of three electrometers; and answers three different purposes, namely, a Henley's electrometer, Lane's discharging electrometer, and Brooke's steelyard electrometer; the first not improved, but the two last, which were very defective when first invented, I flatter myself are here brought to perfection. As the only use of Henley's electrometer to this instrument is, as I have said before, to shew by its continuing to increase in divergency that the battery continues to receive a still stronger charge, it required no improvement; but Lane's electrometer, in its primitive state, could by no means answer the required purpose for batteries, because the ball intended to discharge the battery, was necessarily placed so near to the ball of the battery, that dust and fibrous particles were always attracted by and adhered between the two balls, so as to retard the charging, and often render a high charge impossible: whereas, in this, they are placed at four inches asunder; and when the desired height of charge is obtained, and not before, the ball of the electrometer moves of itself nearer to the ball which is connected with the outside of the battery, and causes a discharge. The defect in Brooke's steelyard electrometer were, 1st, that it could not cause a discharge, and 2ndly, the difficulty of observing the first separation of the balls caused. great error. If it were not placed in an advantageous light (which the nature of the experiments could not always permit), it would not be seen, without the attention of an assistant, which is sometimes unpleasant, and cannot always be commanded. But the instrument which I have described requires no attention or assistance, for as soon as the separation takes place between в and b, the ball a descends, and discharges the battery of itself.

By this combination of improvements, we possess in the present instrument all that can ever be required of an electrometer; namely, by k, we see the progress of the charge; by the separation of в b,

* A chain, or wire, or any body through which a charge is to pass, must be hung to the hook at m, and carried from thence to the outside of the battery, as is represented by the line N.

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