e discovery of this error.
See mariner's compass.
The dip of the magnet was discovered by Robert Norman, 1576.
See magnetometer.
The magnet worn by Sir Isaac Newton in his ring weighed only 3 grains, yet was able to take up 746 grains, or nearly 250 times its own weight.
Artificial magnets were made by Dr. G. Knight ispecific gravities.
This was written about the time of Roger Bacon, 250 years before Da Vinci, 350 years before Porta, and more than 400 years before Galileo and Newton.
The Phoenicians circumnavigated Africa in the seventh century B. C., as we learn from Herodotus.
Strabo (writing about A. D. 18) says:—
If the extent of teet.
It vitrified pumice, slate, tiles, shells, pieces of crucibles; lighted green wood instantly, and dissolved an alloy of lead and tin like so much lard.
Newton's mirror had 7 concave glasses, each 11 1/2 inches in diameter; one in the center, the others encircling it, so as to have a common focus.
The diameter was 34 1/
This mirror being set at an angle of 45°, the perpendicular line of the telescope will become a horizontal line, that is, a line of level.
Invented by Cassini.
See level.
Re-flect′ing-mi′cro-scope.
A form of microscope first proposed by Newton, in which the image formed by a small concave speculum may be viewed either by the naked eye or through an eye-piece.
Owing to the difficulty of illuminating the object, it was long disused, but has been revived by Professor Amici, who places thot sufficiently so to render the rays reflected from a divergent; they are therefore brought to a focus just in front of the large speculum, forming an inverted image which is viewed by the eye-tube.
In the Newtonian form (C), invented by Sir Isaac Newton, 1669, the rays falling on the concave speculum a are intercepted before being converged to a focus by the small plane mirror b, placed diagonally in the main tube, which reflects the image to the eye-piece inserted in the side of the tube.
