There is a slight annual variation in the distance. July 1, 1882, it will be 1° 19' 20". If from this latter quantity the observer will subtract 16" for 1883, and the same quantity for each succeeding year for the next four or five years, no error so great as one-quarter of a minute will be made in the position of the meridian as determined in the summer months. If winter observations are made, the distance in January should be used. The formula for computing the angle of elongation is easily made by any one understanding spherical trigonometry, and is this: R x sin. Polar dist. --------------------- = sin. of angle of elongation. cos. lat. As an example, suppose the time is July, 1882, and the latitude 40°. Then the computation being made, the angle will be found to be 1° 43' 34". A difference of six minutes in the latitude will make less than 10" difference in the angle, as one can see by trial. Any good State or county map will give the latitude to within one or two miles--or minutes. The facts being as here stated, the absurdity of the Ohio law, concerning the establishment of county meridians, becomes apparent. The longitude has nothing at all to do With the meridian; and a difference of _six miles_ in latitude makes no appreciable error in the meridian established as here suggested, whereas the statute requires the latitude within _one half a second_, which is _fifty feet_. There are some other things, besides the ways of Providence, which may be said to be "past finding out." It is not probable that a surveyor would err so much as _three_ miles in his latitude, but should he do so, then the error in his meridian line, resulting from the mistake, will be _five seconds_, and a line _one mile_ long, run on a course 5" out of the way, will vary but _an inch and a half_ from the true position. Surveyors well know that no such accuracy is attainable. R. W. McFARLAND, * * * * * ELECTRO-MANIA. By W. MATTIEU WILLIAMS. A history of electricity, in order to be complete, must include two distinct and very different subjects: the history of electrical science, and a history of electrical exaggerations and delusions. The progress of the first has been followed by a crop of the second from the time when Kleist, Muschenbroek, and Cuneus endeavored to bottle the supposed fluid, and in the course of these attempts stumbled upon the "Leyden jar."