1687 - Science

Science

Philosophia naturalis principia mathematica by Isaac Newton establishes laws of gravity and universal laws of motion, dealing a mortal blow to the strong distinction made by Aristotle between earthly and cosmic phenomena (see Leibniz, 1684). The first law: if an object is moving at a steady speed in a straight line and not pushed or pulled, its velocity will naturally remain constant (it will continue moving at a steady speed in a straight line). The second law: the velocity of a moving object will accelerate if force is placed upon it, and if pushed twice as hard it will accelerate twice as much, but if its mass is doubled it will accelerate half as much. The third law: for every action there is an equal and opposite reaction (see Heron of Alexandria, 76). The late French astronomer Jean Picard found that the length of arc on a great circle corresponded to 1°, and Newton has used this discovery in his theoretical applications to prove that the attraction of the Earth is the principal force governing the motion of the moon in its orbit. Astronomer Edmond Halley, 31, has inspired Newton to write The Principia and has had it published at his own expense (see Halley, 1705).

Astronomer Johannes Hevelius dies at his native Gdansk (Danzig) January 28 (his 76th birthday). Edmund Halley visited him in 1679 with a sextant having telescopic sights, and he showed Halley that he could determine stellar positions quite as accurately without a telescope.