cloud, he could not now get the electric fire to strike the point, though the point was almost in contact with the ball c; but when it was about half a tenth of an inch distant from it, then the electric fire ran in a very small stream to the point; but beyond that distance, though moved very gradually, it was only luminous, and continued so at the point all the while it was gradually removing to the distance of six feet from the ball c, at the end of the artificial cloud.

Exp. 5.-The apparatus still remaining, only changing the wire for the ball of four inches diameter, used in the first experiment, having now a small hole through it. Mr. Nairne then put into this hole a wire, leaving the end, which terminated in a fine point, projecting out only a tenth of an inch beyond the surface of the ball, and directly pointing to the ball c: on charging the artificial cloud, the ball with the point being first placed nearly in contact with the ball c, it was then gradually removed; but not at any distance would it strike to the ball, or the point projecting out of it. The point was luminous at the distance of thirty inches.

Exp. 6. Every thing remained the same as in the last experiment, except only that he now pressed in the point, till it was even with the surface of the four inch ball: on charging the artificial cloud, the electric fire now struck to the ball at any distance, from being nearly in contact, all the while it was very gradually removed to as far as seventeen inches and a quarter; though before in the last experiment, where the point projected from the ball only the tenth of an inch, it would not strike at any distance.

Exp. 7.-The apparatus remaining as in the last experiment, Mr. Nairne took a ball of three and a half inches in diameter, which had a small hole through it, and screwed it to a hollow brass stem. He then put into this hole one end of a wire, and the other end, which was pointed, projecting one inch beyond the surface of the three and a half inch ball. This ball and stem, with the pointed wire to it, he fixed to a stand covered with tinfoil; having a good metallic communication with the earth; he placed this stand so that the point was directly opposite to the side of the artificial cloud, and exactly at five feet distance from it: then on charging the artificial cloud, the greatest striking distance from the ball c to the ball of four inches diameter on the receiving rod D, was found to be sixteen inches and seven-tenths.

Exp. 8.-Every thing continued as in the last experiment, only now he drew the wire out of the ball and stem so far that the point projected nine inches beyond it; on charging the artificial cloud, the greatest striking distance now was found to be six inches and three-tenths.

Now, in order to see how far a point, or different sized balls fixed on the stand, and having a very small separation in the metallic communication with the earth, would visibly act to carry off the

electric fire of the artificial cloud, Mr. Nairne made the following experiment:

Exp. 9.-He took a stick of common sealing-wax, and having fixed a screw to each end, he pasted a slip of tinfoil the whole length of the surface, and having made a separation in the foil of about a fiftieth of an inch, he screwed the pointed wire into one end, and the other end of the wax to the brass rod, where the ball with the point projecting from it was placed in the last experiment. He also removed the other stand with the ball, to which the artificial cloud likewise struck in the same experiment; the artificial cloud was then charged, and the stand being placed in such a manner that the point was directly opposite to the side of the artificial cloud, it was then removed till he found the distance at which the light between the separation of the tinfoil no longer became visible. This distance of the point on the wax was above seven feet, how much farther it might have been luminous he had no opportunity of trying, this distance being the farthest he could remove it in his room, and under the disadvantage of having the end of the artificial cloud within thirty-three inches of the edge of the wainscot. When a ball of three-tenths of an inch was put in the place of the point, the light was visible at the distance of four and a half feet, but with a ball of three inches diameter. only at two feet.

Exp. 10. Mr. Nairne took another stick of sealing-wax, one and three-tenths of an inch diameter, and about ten inches long, and pasted on it round pieces of tinfoil of half an inch in diameter, at about half an inch distance from each other. One end of this stick of wax was screwed to the receiving rod D; and into the other end was screwed the pointed wire used in the fourth experiment. He then laid a piece of brass on this wax, so as to connect all the separations of the round pieces of tinfoil except two; then the point of this wire on the wax was placed nearly in contact with the ball. On charging the artificial cloud the electric fire now struck to the point, and continued to strike to it all the while it was gradually removed to the distance of one and one-tenth inch, beyond that distance it would not strike, but the point continued luminous till it was removed to the distance of three feet.

Exp. 11. The apparatus remaining as in the last experiment, he only took away the piece of brass which laid on the wax to connect the pieces of tinfoil together. The charged artificial cloud did not now strike to the point till it was removed from the ball c to the distance of four and a half inches; it then began to strike to it, and continued striking while it was gradually removing sometimes to ten inches; but when the point was removed beyond the greatest striking distance, the point was not luminous as in the last experiment, except when the artificial cloud discharged its electric fire out into the air, in a diverging pencil from the ball c: it was then luminous, but at that instant only. Every time the artificial cloud struck to the point, the electric fire made a beautiful appearance in

passing off between the separation of the pieces of tinfoil. Mr. Nairne then connected all the tinfoil on the wax, so as to leave no separation; then the charged artificial cloud would not strike to the point at any distance.

Exp. 12. Mr. Nairne placed the rod D, with the four-inch ball at the end, as in the first experiment: this he put on a glass pillar to insulate it; then from the rod he made a communication to the earth, with about three feet of silver wire, which was only one eight-hundredth part of an inch diameter: on charging the artificial cloud, it struck to the ball D, as in the first experiment, viz., seventeen inches and four-tenths.

Observation 1.-From the first three experiments it appears that the artificial cloud strikes at distances greater as the termination of the conductor is more blunted, or as it terminates with the larger ball; and that the striking distance is less as the ends of the conductor tend more to a point; and in the fourth experiment, that when the end of the conductor is pointed, the point is not struck at any distance whatever, but continues luminous to a certain distance, carrying off silently the electricity of the artificial cloud. It seems from these experiments, that pointed conductors are to be preferred before those terminating with a large ball: the pointed one depriving the cloud silently of its electric fire, whereas the ball receives the electric fire in a strong spark. And in the fifth experiment, where a point projects but one-tenth of an inch, from a ball of four inches diameter, neither the ball, nor point projecting from it, is struck at any distance. This seems to show the utility of a pointed rod, even if it projects but a small distance above the highest part of a building. The sixth experiment shows, that a point within the surface of a ball does not prevent the ball being struck. The seventh and eighth experiments likewise show that our artificial cloud strikes to a ball of four inches diameter, only at the distance of six inches and eight-tenths, when the point is drawn out nine inches from the three and a half inch ball, placed opposite to the side of the artificial cloud; and that when the point projects only one inch, that then it strikes to the four-inch ball at sixteen inches and four-tenths distance.

May we not from these two last mentioned experiments conclude, that the more elevated our pointed conductors are, the greater is the chance of preserving our buildings from the effects of lightning? For here the point being elevated or projecting nine inches out of the ball, representing the highest part of a building, was found continually depriving the artificial cloud of its electric fire to such a degree that it would not strike half the distance that it did when the point was elevated only one inch. And from the ninth experiment we learn, that the conductor terminating in a point acts at a far greater distance than one terminating with a ball, in carrying off the electric fire, or matter of lightning, from the artificial cloud. And though the point was luminous so far, yet there was no distance whatever at which the artificial cloud would strike to it.

From the tenth and eleventh experiments we learn, that the metallic part of the conductor being separated or discontinued is the reason that the artificial cloud strikes to the point; and that it strikes farther to the point as the number of the separations are increased; and that if the metallic communication with the moist earth be made complete, then the charged cloud will not strike to the point. When a conductor to a building, terminating in a point, has been struck, Mr. Nairne thinks that there had not been a complete and sufficient metallic communication with moist earth and from all the accounts he had met with, this seems to have been the cause of their having been struck. From the twelfth experiment we learn that a very fine wire will conduct a strong spark.

Mr. Nairne contrived another moveable artificial cloud: it consisted of a hollow tube of wood, with a ball at each end, being together about six feet in length: from each end was suspended a light hollow wooden cylinder; these with the balls and tube were covered with tinfoil: it was placed with its axis resting on two semi-circular hollows in a piece of brass fixed on a glass pillar, by which it was insulated it moved very easily on its axis, and was brought to a horizontal position by means of two moveable pieces.

Exp. 13. Mr. Nairne first put this moveable artificial cloud into a horizontal position, and placed it so that the brass on which the axis rested, was in contact with the end of the artifical cloud. Then, under each of the hollow cylinders he placed a stand, having a good metallic communication with the earth. On one of the stands was put a pointed wire, the same as was used in the fourth experiment; and on the other, a brass ball of three inches diameter. He then placed the point and ball each twelve inches from the middle of the bottom of the corresponding hollow cylinder: on charging the artificial cloud (which consequently charged the moveable artificial cloud in contact with it) the point was luminous, and the moveable artificial cloud still remained in a horizontal position, though there was now a point under one end and a ball under the other; and on ceasing to charge the two clouds, it was found directly after, that the point had drawn off almost all the electric fire from both.

Exp. 14. The two clouds being charged, he took away the stand with the three inch ball on it: the point remained luminous, and the moveable artificial cloud still continued horizontal, not being attracted to the point, though there was now the stand with the pointed wire under one end of it: the point having carried off the electric fire as in the last experiment.

Exp. 15.-The two louds being again charged, he replaced the stand with the ball on it: and now, instead of taking away this stand, as he did in the last experiment, he took away the stand with the pointed wire on it: the consequence was, that the end of the moveable artifical cloud was now attracted down to the ball till it came to its striking distance, where it then discharged its electricity on it in a strong spark. The moveable artificial cloud then receded

a little till it was charged, and then was attracted by the ball as before, till it came to its striking distance, when it again discharged its electricity at once, and so continued striking, and then receding to a little distance, as long as the two clouds were charged.

Exp. 16.-The moveable artificial cloud continuing to strike to the ball as in the last experiment, he now replaced the stand with the pointed wire on it: then immediately the point became luminous, and the moveable artificial cloud ceased striking to the ball, and soon returned to its horizontal position as at first.

Exp. 17. The apparatus remaining as in the last experiment, and the two clouds continuing to be charged, he took away the stand with the point; then the moveable artificial cloud was attracted down to the ball; and struck as before. He then placed the stand with the point close to the stand with the ball; on which the point became instantly luminous, and immediately the moveable artificial cloud ceased striking, soon returning from the ball and settling nearly in a horizontal position. There the point carried off the electric fire as in the thirteenth and fourteenth experiment.

Observation. From the thirteenth experiment, with the point under one end of the moveable artificial cloud, and a three inch ball under the other end, it seems as if neither the ball nor point attracted either end; or that they both equally attracted, or repelled each end, as in either case the moveable artificial cloud would remain horizontal. And in the fourteenth experiment, in order to try whether the point would attract or repel the moveable artificial cloud, the ball was taken away, and only the point was left under one end, as now all the action of the point either to attract or repel would be exerted on that end which was now over the point, and consequently that end should either be attracted down to it, or repelled from it: but from the experiment it appears, that the point drew off all the electricity silently, without either attracting or repelling the end of the moveable artificial cloud which was over it, as it continued horizontal all the time it was charged.

The fifteenth experiment was made to see if the ball would either attract or repel the moveable artificial cloud, as in this experiment the ball only was under one end, and every thing else exactly the same as when the point only was under. But here we find the effect of the ball very different from that of the point; for instead of drawing off the electricity silently, as the point did, without attracting the end of the moveable artificial cloud, on the contrary, the moveable artificial cloud was attracted down towards the ball, till it came within striking distance, where it discharged its electric fire all at once on the ball with a loud and strong spark. And again, in the sixteenth experiment, where the stand with the point is replaced at the other end, while the cloud was attracted down to the ball, it instantantly prevented its striking to the ball by carrying off the electric fire as fast as the moveable artificial cloud received it from the artificial one. And from the seventeenth experiment we