An Electroscope Made of a Board and An Old Walking Stick.

Progress, Volume VI, Issue 11, 1 September 1911, Page 800

An Electroscope Made of a Board and An Old Walking Stick.

A sensitive electroscope, with which the elementary laws of electrical attraction and repulsion can be satisfactorily demonstrated, may be made very easily of the commonest materials, with practically no expense. The materials and the mode of construction may he varied indefinitely. The following simple and interesting method is suggested by a writer in “Die Gartenlauhe”: The stand of the electroscope is constructed by driving the end of an old walking stick tightly into a hole bored for the purpose in the centre of a square piece of hoard, to the under surface of which three small blocks of wood have been glued or tacked to serve as feet, so that the combined board and cane will stand firmly on the table, with the cane vertical. Most articles of furniture have four feet, and this is the i eason why they do not stand firmly. Scientific instruments are always mounted on three feet. A fibre of unspun silk is tied at its middle about one end of a light wooden rod, say twelve inches long. The silk fibre is then stretched tightly between the nails driven into the can and its ends are tied to the nails. The upper nail is connected with the free end of the rod by a second fibre of such length that the rod is supported in a horizontal position.

The free end of the rod must now be furnished with a very light ball or knob. Two natural vegetable products are singularly well adapted for this purpose. One is the oak-gall, the other the fungus called the puff ball, which abounds in the woods in many districts. The puff ball is

filled with a fine yellow powder which is scattered by the slightest pressure. This powder must not be allowed to enter the eyes, for it may cause severe inflammation. A puff ball of the size of a small apple is impaled on the end of the wooden rod and is painted with gold bronze, not for ornament, but to give the ball a surface that will conduct -electricity. The cost of the gold bronze (a few cents) is the only expense which has been incurred in constructing the electroscope, which is now complete. T e will begin our experiments by rubbing a glass tube or bottle vigorously on the coat sleeve or with a woollen cloth and thus electrifying it, and holding it near the gilded puff ball. The ball immediately moves toward the glass by swinging the horizontal arm round its axis, the vertical silk fibre. This experiment shows that glass, electrified by rubbing with a woollen cloth, attracts an electrified body, the gilt ball. If a hard rubber penholder is rubbed in the same way and brought near the ball, precisely the same result will follow.