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115.

[[image:  drawing of a masonry wall cross section E A D O with a beam A B C D projecting perpendicularly out to the right with a weight L suspended from C. A dotted line I down the center-line of the beam, and marks G and H above and below the dotted line.]]

This being supposed if A B C D is a stick square fastened in a wall we may conceive that from D to I wch is half of ye thickness A D, ye parts are pressed by ye weight L, those wch are near to D more than those towards I, and that from I to A they are extended, as hath been explained, and we may apply the reason to ye cords at ye part I A;  whence it follows that as ye length I G is to L of ye thickness I A so shall ye force of ye weight L be augmented to break ye solid, and as there is need of greater force to press ye parts towards D than towards H, if we suppose that that force is diminished according to a series of numbers from a unite there will be moreover need of the same proportion of ye length I F to 1/3 of ye largeness D I to make ye pressure and as it is probable, that these pressings resist as much as ye extension and that there is need of ye same weight to make them these extensions, and these compressions part ye force of ye weight L adding ye third of thickness I A to ye third of ye thickness I L, ye whole shall be equal to ye third of the whole thickness, A D whence will follow ye same thing as if all ye parts were extended:  Therefore to reduce ye extension towards ye point A to a rupture, it is necessary that ye weight L be a little more than 10 pounds to break ye solid A B C D, if ye length C D is to ye third of ye thickness as 1 to 30, and that there is need of a little more than 300 pounds to break it by drawing it downwards:  For ye same thing ought to happen in respect of ye effort of ye weight, as if ye parts between I D were extended as ye superior.

I have experimented with Mr Hubin that a threed of glass of 1/4 of a line thick and 4 foot long was extended 4/3 of a line without being broken, and litting it ruturn to itself it regained its first extension;  we extended also 3 of ye same thickness wch broke, being extended to 1 1/2 line.  To know it there was at ye two ends of each thread a bowl of glass of two or 3 lines, we engaged one of these bowls between two tenter hooks stroke into ye end of a table almost to their halfs, so that pushing them very strongly we could not sensibly shake them, and by consequence ye gross end of ye thread being well engaged by ye bottom of ye tenters could not approach towards ye other end of ye table, there was 3 small pinn holes made to discern ye elongation, ye thread was held upon ye table at its length, but drawing it moderately with ye hand, and drawing it stronger it to ye second hole, and drawing it yet more to ye third, and a little relaxing ye effort, it would return to ye 2d or 1st hole.  To do it well it was necessary that one of its ends should be pushed into a hole of a small peice of iron, and that ye other should be tyed to 2 or 3 small [[strikethrough]] cords [[/strikethrough]] cords wch being joyned together made but one, wch was wound about a peg of a lute or some other instrument to extend ye thread by turning by little and little.  There was made marks to know ye elongation, and so we might make ye thread of glass like a cord of a virginal.

This being supposed here is ye experiments wch I made concerning ye resistance of solids these rules may very well prove Architectures for ye beams out gettings &c.

Transcription Notes:
virginal - an early spinet with the strings parallel to the keyboard, typically rectangular, and popular in 16th and 17th century houses. mandc: Reviewed and revised the image description (same as page 117), changed J's to I's.