Take a small phial and coat it, about three inches up the outside, with tin-foil. At the mouth of this phial cement a metallic cap, having a hole with a valve; and from this cap let a wire proceed a few inches within the phial, terminating in a blunt point. When this phial is exhausted of air, a metallic ball must be screwed upon the cap, so as to defend the valve, and prevent the air from getting into the phial. The reason why this phial requires no inside coating, is, because the electric fluid pervades a vacuum, so that it can pass very easily from the wire to the surface of the exhausted glass, without the assistance of a non-electric coating. This phial exhibits very plainly the direction of the electric matter, both in charging and discharging, for if it be held by its bottom, and the ball be presented to the prime-conductor, positively electrified, you will perceive that the pencil of rays (which always appears when the body is positively electrified, or is giving out the electric matter) will proceed from the wire within the phial, and when it is discharged, the star, (which always indicates that the body is negatively electrified, or is receiving the electric fluid) will be seen on the point instead of the pencil, but if the phial be held by the ball, and its bottom be presented to the prime-conductor, the contrary will take place. _The luminous Conductor._ This instrument, as well as the preceding, is an invention of Mr. Henley’s and also shows the direction of the electric fluid passing through it. The description of it is as follows. To each end of a glass tube, about eight inches long and three or four inches in diameter, is cemented a metallic cap, so as to be perfectly air tight. A point projects from one of the caps, by which it is to receive the electricity from an excited cylinder, and from the other proceeds a wire, terminated by a ball, from which sparks may be taken. Each cap is furnished on the inside with a knobbed wire, which extends some distance into the tube. A stopcock or valve must be adapted to one of the caps, by which the tube may be exhausted of air. The supporters of the instrument are two glass pillars, fastened to a bottom board. When the tube is exhausted of air, and its pointed end placed near the excited cylinder of an electrical machine, the point will appear illuminated with a star, and a weak light will be seen pervading the whole tube; but from the knobbed end of the wire, within the tube, a lucid pencil will issue, and the opposite knob will be illuminated with a star or round body of light, which, as well as the pencil of rays from the other knob, will be discernible among the other light which occupies the cavity of the tube. If the point, instead of being presented to the cylinder, be connected with the rubber, the appearance will be reversed—the reason is too obvious to mention.