Page:Popular Science Monthly Volume 10.djvu/168

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ors, and, since to connect a telegraph-wire with the conductor would render the telegraph useless, no telegraph from without should be allowed to enter a powder-mill, though there may he electric bells and other telegraphic apparatus entirely within the building.

I have supposed the powder-mill to be entirely sheathed in thick sheet-copper. This, however, is by no means necessary in order to prevent any sensible electrical effect taking place within it, supposing it struck by lightning. It is quite sufficient to inclose the building with a network of a good conducting substance. For instance, if a copper wire, say No. 4, B.W.G. (0.238 inch diameter), were carried round the foundation of the house, up each of the corners and gables and along the ridges, this would probably be a sufficient protection for an ordinary building against any thunder-storm in this climate. The copper wire may be built into the wall to prevent theft, but should be connected to any outside metal, such as lead or zinc on the roof, and to metal rain-water pipes. In the case of a powder-mill it might be advisable to make the network closer by carrying one or two additional wires over the roof and down the walls to the wire at the foundation. If there are water or gas pipes which enter the building from without, these must be connected with the system of conducting-wires, but, if there are no such metallic connections with distant points, it is not necessary to take any pains to facilitate the escape of the electricity into the earth.

Still less is it advisable to erect a tall conductor with a sharp point in order to relieve the thunder-clouds of their charge.

It is hardly necessary to add that it is not advisable, during a thunder-storm, to stand on the roof of a house so protected, or to stand on the ground outside and lean against the wall.—Nature.



DURING a recent visit to Salt Lake City I happened to ask one of the leading Mormons what works, in addition to the Book of Mormon, would give me a fair idea of the religious doctrines professed by the Latter-day Saints and of their history, as they themselves desire to have it told. The gentleman addressed most kindly offered for my acceptance several books, among which were pamphlets by Orson Pratt, one of the twelve apostles of the church, the "Key to the Science of Theology," by Parley P. Pratt, and the "Rise, Progress, and Travels of the Church of Jesus Christ of Latter-day Saints," by President George A. Smith.

So far as religious tenets are concerned, the authority of the works