Page:Philosophical Transactions - Volume 003.djvu/64

 when the Liquor falls between the heads, which are supposed erect to the Horizon.

2. The Mensuration or Plaining of the Surfaces of divers Solids and Spiral Spaces, unknown to Antiquty, and not treated of by any modern Authors, till of very late years; from whom the Author differs in his Method: Particularly he finds a Circle equal to the Surface of

Generally Prop., 36. The Surface of every Round Solid is equal to a Rectangle, whose Base is the Circumference of the Figure, by the Rotation whereof the Solid is begot, and the Height equal to the Circumference, which the Center of Gravity of the Perimeter of the Figure describeth.

3. A Method for strenghtening of Curved lines in the first 6 propositions; and in particular he finds a Right line equal to a parabolical Curve, Prop. 51

4. Divers Optick Propositions towards the end of the Book, concerning the Imperfection of the Eye, and the Confusion of the Sight; the apparent Magnitude of the Sun, low and high; the Tails of Comets; what Proportion the Earths illumination by the Sun at the Full of the Moon bears to the illumination of the Earth by the Moon; and the like comparison between the Sun and Sirius; That vision by aid of a Telescope or Microscope, is not deceitful: And an Observation of the likeness between the Earth and the Moon.

This same Author in his Letter to Mr F. C. suggests, that Cassini hath observed the Motion of Jupiter about his Axis in 10 hours; of Mars in 23 hours; that Venus hath the like Rotations: but the precise period not yet known; that Cassini Rh