VARIATION OF THE NEEDLE.

It is thought by some surveyors that a change has taken place in the variation of the needle, and that the power of attraction is returning to the east or right hand. For my own satisfaction, I have for some years past been endeavouring to ascertain the truth of the fact, and my observations for the last ten years past require only 20' to be added to strike the former object. It is well known that formerly surveyors made an allowance to the west or left hand, of one degree, for every 10 or 11 years for variation, and it now comes short 40' of the common allowance, so that from the result of my observations it appears evidently that the variation is not on the return, but still increasing, but so slow and variable every year, that it cannot be ascertained, unless by a series of experiments. To corroborate the following observations, I would remark, that I have lately read (I think in the Encyclopædia) of a curious gentlemen in London, who with a nice instrument, monthly for a number of years, made observations upon the variation, and he seldom found the needle cut the same degree and minutes, but varying sometimes to the right, others to the left: sometimes more, sometimes less, which shows that the attractive power is variable.

On the 18th of July, 1810, an object on the North mountain, 3 and a half miles off, bore

N. 61° 00' W.
8th July, 1811,the same object bore6050
14th July, 1812,do.6050
10th July, 1813,do.6050
8th July, 1814,do.6110
12th July, 1815,do.6115
13th July, 1816,do.6115
15th July, 1817,do.6115
14th July, 1818,do.6130
15th July, 1819,do.6125
10th July, 1820,do.6120

From whatever cause the variation of the needle arises, it evidently is affected by a something within our earth; but whether from the motion of two attractive poles, or four, as has been maintained by great men, or whether by a concentric globe of elementary particles composed of electricity and refined iron, adjusted and organized in a particular way, are all hypotheses. The phenomenon of the dipping needle is a curiosity, and sufficient to satisfy us that the power of attraction is about the centre of the earth, for let a needle be truly balanced on a centre pin in our latitude, then give it the polarity necessary, the north end will dip about fifty degrees;—move it to the equator it will become again level;—carry it still southward, the south end will dip.

When effects are obvious, man more curious than wise, endeavours to search out the cause, and in some things we may be successful,—others are beyond our knowledge, and hid in the mysteries of Nature's God.

John King.

Mercersburgh, (Penn.) }
July 18, 1820. }