CV
the cover is removed, its electricity will be positive, that of the
form negative.
4) a. Place the cover on it, touch at first with one finger
the cover and then with another one the form and a stroke will be
felt,
b. If after that the cover is removed, we get a positive
spark from it. Explain all these phenomena.
§ 265. b) The Electroscope, a simple instrument (invent
ed by Volta in 1775) for ascertaining whether bodies are elec
trified or not, 427. It consists of a glass bottle, the neck
closed by a cork; a brass rod terminating at its upper extremity
in a knob and at the bottom of the flask in two strips of gold
leaf; of course the rod must be insulated. How can the
existence of electricity be ascertained by this instrument?
§ 266. c) The Electric Machine, about its form and
management see: 430. No. 107. It consists
1) of a disc or cylinder of glass.
2) Two amalgamated (1 part of tin, 1 part of zinc and 2
parts of mercury) cushions.
3) The conductor of the disc and that of the cushions (iso
lated balls or cylinders of metal).
4) Two brass rods, provided with a series of points in the
sides opposite the glass and fixed to the conductors.
§ 267. a.) The Leyden Far, an instrument for collecting
and condensing electricity. 429. This jar, discovered by Kleist
in Kamim and Mushenbröck in Leyden 1745, consists of a glass-
bottle, the interior part and the outside of which are coated up
to a certain distance from the neck with tinfoil; a brass rod
ending in a knob communicates with the metal inside.
It may charge itself; how? It may be discharged by touch
ing alternately the knob and the external tinfoil; explain.
