The longitude may in some places be found by the variation of the needle; and Mr. Churchman, of America, having given much attention to the subject, comparing the observations of others, and many of his own, thinks that he has found a method of determining the longitude to a great degree of certainty, in most cases, by this means.
He says there are two magnetic poles of the earth, one to the north and the other to the south, at different distances from the poles of the earth, and revolving in different times; and from the combined influence of these two poles he deduces rules for the position of the needle in all places of the earth, and at all times, past, present, or to come.
The north magnetic pole, he says, makes a complete revolution in 426 years, 77 days, 9 hours, and the south pole in about 5459 years. In the beginning of the year 1777 the north magnetic pole was in 76 deg. 4 min. north latitude; and in longitude from Greenwich 140 deg. east; and the south was in 72 deg. south latitude, and 140 deg. east from Greenwich.
LECTURE XXXIV.
Of Electricity.
Electricity is a property belonging to, or capable of being communicated to, all substances whatever; and whereas by some of them it is transmitted with great ease, and by others with much difficulty, they have been divided into two classes, and denominated conductors or non-conductors of electricity. Also the latter receiving this power by friction, and other means, are termed electrics, and the former non-electrics.
Metals of all kinds, and water, are conductors, though in very different degrees; so also is charcoal. All other substances, and also a perfect vacuum, are non-conductors of electricity. But many of these substances, when they are made very hot, as glass, resin, baked wood, and perhaps all the rest on which the experiment can be made in this state, are conductors.
It is the property of all kinds of electrics, when they are rubbed by bodies different from themselves, to attract light substances of all kinds, to exhibit an appearance of light, attended with a particular sound, on the approach of any conductor; and if the nostrils are presented, they are affected with a smell like that of phosphorus. This attraction is most easily explained by supposing that electricity is produced by a fluid exceedingly elastic, or repulsive of itself, and attracted by all other substances.