Then he turns to animals. Two cats, "each four months old, of nearly the same size, and fed alike," are placed in cages, one of them being near the conductor of the electric machine, which is excited for some hours. Both the electrified cat and the non-electrified cat lose weight, but the electrified cat loses the most, about 54 grains. Nollet thinks this may be due to "difference in temperament," although he admits that the cats went placidly to sleep, except when he gave them shocks. Then he electrifies pigeons and small birds, and finally persons, and concludes that in all cases there is a loss in weight due to "transpiration;" but when he attempts to treat actual maladies he fails. "The paralytics, experiencing no relief which would sustain their patience (for some is necessary in order that they may undergo this sort of torture), complained bitterly," and the Abbé abandons for the time his high hopes of thus relieving suffering humanity.

The great majority of experiments now contemporaneously recorded, however, are of little interest. A better idea of the thought and achievement of this period can be had by following the work of a few men, whose superior intelligence, or better facilities, or both, led their thought, for a short time only, to bring forth all the fruit that is worth garnering.

Winkler discovered that when electricity had several paths to choose from, it appeared to traverse the one which was composed of the material which conducted best, and that is all that need be said now about him. The two philosophers who most attract and hold attention are rivals -Louis Guillaume Le Monnier, the younger, in France, and Dr. William Watson in England. At this time no one pretended to understand why the Leyden jar behaved as it did. First, it could be electrified by the ordinary globe machine or rubbed tube; second, it yielded an extraordinarily strong shock and bright spark; and third, it did this last only when its exterior was connected in circuit with its interior. In entering upon a new inquiry, it is often

LE MONNIER'S CIRCUIT.

531 as efficacious, for the purpose of starting, to challenge an existing theory as to propound a new one. Thus did Le Monnier. Dufay had stated in substance that conductors cannot be electrified unless supported on non-conductors. The Leyden jar, says Le Monnier,' must be an exception to Dufay's principle, for it can be electrified, although it is supported on the hand, which is a conductor. That shows us, at once, that Le Monnier-and he probably reflected the idea of the French philosophers generally—simply considered the jar as an electrified mass, regardless of its diverse materials. For him the objective point is less the jar, than the circuit. He states the principle of it: “All bodies are electrified by means of a vial of water fitted to a wire," if "placed in any curved line connecting the exterior wire and that part of the bottle which is below the surface of the water"-but passes at once to something remarkable. Hitherto everything to be electrified was insulated on pitch cakes or silk supports. What astonishes Le Monnier now is, if 200 men be placed hand in handthe end individuals touching the inserted wire and the bottom of the bottle respectively—a violent concussion is felt by all at once; and this equally well, whether they are all mounted on cakes of resin or stand on the floor; equally well when they are connected by iron chains; equally well whether the chains dip in the water or lie on the ground, and the electricity runs equally well-now he abolishes the men-through a wire a league long, "though a part of it dragged on the wet grass, went over charmel hedge or palisades and over ground newly ploughed up." He even bends a bar of iron to touch the two points of the jar, and observes that it does not acquire more electricity when held by silk lines than when supported in the hand. Strange, he thinks, how "the electricity will stay in the path thus made for it, without either running off or becoming absorbed."

1 Phil. Trans., No. 481, p. 247, 290. Memoirs de l'Acad. Roy. des Sci.,

There was an ornamental octagonal pond in the Tuileries gardens of those days, which measured about an acre in extent. Around the semi-circumference of this Le Monnier disposed an iron chain so that its ends came diametrically opposite one another. These ends were held respectively by two observers, one of whom dipped his disengaged hand in the water. The other, across the basin, held in his free hand an electrified Leyden jar, the inserted wire of which he thus presented to an iron rod which entered the water, and was supported on a cork float. Thus early in 1746, a circuit was made including both water and a metallic conductor, over which passed the discharge of the jar, so that the two observers were simultaneously shocked.

Like other experimenters who had dealt with long conductors, Le Monnier sought to measure the velocity with which the electric matter ran over them, but without avail; nor was he any more successful in finding out what impelled it at a speed which he estimates to be at least "thirty times that of the velocity of sound in air." He made up his mind, however, that the electric matter is communicated to bodies in proportion to their surfaces, and not in proportion to their masses.

The conclusions of Le Monnier appear to have been regarded by the English electricians as a challenge. Watson was now their leader, and his response was ready. Le Monnier had dealt with the jar as a mere electrified mass, operating to increase the shock or spark, for some reason, unknown. Watson,' in reply, declares that it owes its capabilities to the accumulation of electrical matter within it-this happening because the glass acts as a barrier and prevents the electrical matter escaping from the water as it is supplied thereto by the inserted wire. We shall see changes in these notions soon. Meanwhile, as for the rest of Le Monnier's observations, they merely prove, says Wat

'Phil. Trans., No 482, p. 388. Watson: Exp'ts. and Obs'ns. on Elec'y. 3d ed. London, 1746.

WATSON ON THE LEYDEN JAR.

533 son, "what I have myself found out," that the electricity will always describe the shortest circuit between the electrified water and the wire of the vial which contains it, "and this operation respects neither fluids nor solids, as such, but only as they are non-electric (conducting) matter. Thus this circuit," he adds, tracing it and using the word to name the path provided by Le Monnier, "consists of the two observers, the iron chain, the line of water and the iron rod in the floating cork."

Watson' is now well in the van. The German and the French electricians, preferring to follow the leadership of Winkler and Nollet, are devoting themselves chiefly to contriving variations of experiments already decisive, and so to heaping up a great mountain of cumulative proof. Watson shows that if the amount of water in the jar is increased even to four gallons, the stroke is not augmented in strength; that iron filings therein answer as well as water, and mercury as well as iron filings. The specific gravity of the material in the jar he thus discovers has no influence. He states that the Leyden vial "seems capable of a greater degree of accumulation of electricity than anything we are at present acquainted with . . . by holding its wire to the globe in motion, the accumulation being complete, the discharge runs off from the point of the wire as a brush of blue flame."

Watson now, as the result of all his observations, propounds a theory which was generally accepted by the English philosophers. Historically, and in the light of immediately ensuing events, it is of especial importance.

The hypothesis affirms the existence of an electrical

1Watson's papers of this period in Phil. Trans. are: No. 478, p. 41, read February 6, 1746; No, 482, p. 388, read January 29, 1747; No. 484, p. 695, where there is added to his paper of Februry 6, 1746, “A Sequel to the Experiments and Observations," etc., read October 30, 1746. The principal papers were separately published. Experiments and Observations, 3d Ed., London, 1746. Sequel to Experiments and Observations, 2d Ed., London, 1746: An acccount of the experiments made by some gentlemen of the Royal Society, etc. London, 1748.

ether, much more subtle than common air, and passing to a certain depth through all known bodies. It has the property of air, of moving light objects, and is likewise elastic, this last fact being shown by its extending itself around excited electrics, by its increasing the motion of fluids, by the apparent influx of electrical fire to all bodies and by its giving violent shocks to the human frame.

With this ether all bodies are normally charged. If, however, a body be excited, then the normal conditions are disturbed, so that the ether in the nearest unexcited non-electric tends, by its elasticity, to move to the excited body where it accumulates. In so doing it carries light bodies with it, which accounts for electrical attraction.

Applying this idea to an electrified Leyden jar held in one hand of an observer, who touches with the other the metal gun-barrel on which it is suspended by its inserted wire, Watson maintains that, on the explosion which follows, the man (nearest conductor) instantly parts with as much fire from his body as is accumulated in the water of the jar and in the gun barrel; the fire rushing violently through one arm to the water, through the other to the barrel. Then as much fire as the man has lost is immediately and with equal violence replaced from the floor of the room. Hence, and for both reasons, the shock. This flux, he further says, may be prevented, and its effects are not seen, when the glass containing the water is too thick, or if the man stand on an insulator, or if the points of contact between his (conducting) hand and the jar which it holds are fewer. The last limitation, it may be observed in passing, proved suggestive; for Dr. Bevis, a member of the Royal Society, promptly showed that the greatest number of contact points would be obtained by coating the exterior of the jar with sheet lead or so-called tin foil. This suggestion was adopted, as it was found that a person who merely touched this coating with a small wire obtained as strong a shock as if the whole hand rested against the exterior of the uncoated bottle.