These experiments, though not the most entertaining are certainly among the most important in electricity. By the knowledge of them, mankind have received the greatest practical advantage. But as we have already treated of this subject, we shall, in this chapter, describe only two experiments which may serve to set it in a clearer light, and which may, in a more particular manner, demonstrate the utility of affixing pointed conductors to buildings, in order to preserve them from the dreadful effects of lightning. EXPERIMENTS. _The electrified Cotton._ Take a small lock of cotton, extended in every direction as much as can conveniently be done, and by a linen thread about five or six inches long, fasten it to the prime-conductor; then let the cylinder of the machine be turned—the lock of cotton, by the repellency of its filaments, will immediately swell and stretch itself towards the nearest uninsulated conductor. In this situation, if you present your knuckle or a knobbed wire towards the cotton, it will immediately move towards it, and endeavour to touch it; now with the other hand present a pointed wire to it:—the cotton will immediately shrink up, and fly towards the prime-conductor. Remove the point, and the cotton will again approach the knuckle or knobbed wire—present the point, and it will again recede. This experiment shows that a point is the proper termination for a lightning rod. For the cotton will represent the cloud, and the two wires, the lightning rods with different terminations. The cotton is attracted by the knuckle or knobbed wire, in order to part with its electricity, this however cannot be effected unless they come so near as to touch one another, and then the discharge is effected at once. But the point is capable of drawing off the electricity when at a distance, and it does this gradually; at the same time that it causes a current of air which repels the cotton; the cotton being deprived of its electricity is again attracted by the prime-conductor. _The electrified Bladder._ Coat a bladder that is well blown, with gold, silver, or brass leaf, which may be fastened on with gum water.—Suspend this bladder at the end of a silk thread, six or seven feet long, from the ceiling of the room. Electrify the bladder by giving it a few sparks from a charged jar, and hold towards it, at some distance, a knobbed wire; you will perceive that the bladder approaches the knob, and when it comes within striking distance, gives it the electricity it received from the charged jar, and thus becomes discharged. Touch it again with the charged phial, and instead of the knobbed wire, present the point of a needle towards it, the bladder will now be rather repelled than attracted, especially if the point be very suddenly presented to it. CHAP. V. _Promiscuous Experiments._