Decr. 6th. 1760.
Talked with Zab about Newton, Bacon, Lock, Martin, Chambers, Rowning, Desaguliers, S’Gravesende &c. I told him I had a low Opinion of the Compilers, Abridgers, and Abstract makers. We had better draw science from its fountain in original Authors. These Writers, the Hirelings of the Booksellers, only vend us the Discoveries of other Philosophers, in another form, and under another Title, in order to get Bread to eat and Raiment to put on.—Zab says, that Martin has made several Discoveries—has invented new Machines, improved and perfected old ones, nay has even detected Errors in Newton. E.g. Newton always thought, the Moon was surrounded by an Atmosphere, but Martin proved it is not; because the Starrs, that appear all round it above, below and on each side of it, are not diminished in their Lustre, as they would appear, if the Rays passed from them thro an Atmosphere.
Then we transited to Dr. Simpson , Euclid &c. and he asked me to demonstrate, that the 3 Angles of a Triangle are equal to 2 Right. I undertook it. Draw a right Line, A.B. Erect the Perpendicular, C.D. Draw the Hypothenuse D.A. Parallel to A.D. draw the Line C.E.
Now I say that the 3 Angles ACD., CDA., and DAC are equal to two right Angles. For it is easy to see that DCA., is a right Angle, and that BCE, which is equal to CAD added to ECD, which is equal to CDA, make another right Angle. But how do I know that BCE is equal to CAD? Let the Triangle ECB, be moved along, to the left hand and by the Hypothesis CE will fall upon AD and CB Upon AC, and of Consequence the 2 Angles are equal. How then do I know that the Angle ECD is equal to ADC? See the Dem[onstration] in Euclid.
Then we attempted to demonstrate the 47th of the 1st Book. That the Square of the Hypothenuse is equal to the Squares of both the Legs.
I am astonished at my own Ignorance in the french tongue. I find I can neither express my own Thoughts, in it, nor understand others, who express theirs readily in it. I can neither give nor receive Thoughts, by that Instrument.