The Civil engineer and architect's journal, scientific and railway gazette (1839)
London : [William Laxton] · leaf 401
r, the line of intersection / a will be a straight lineat right angles to the tangent I m. The triangle a I m is therefore the projection of a right angled triangle; and in the short distance/ m the tangent very nearly coincides with the plane of the spiralsurface, hence the angle I a m will be a… … From o where the axis intersects D E in plan draw o u parallel to/ m, meeting P P in j., produce r o to c. In fig. 1 let / a be the pro-jection in elevation of the line / a; join a c and produce it to u, mak-ing I a : a u : : I a : a u. Through u draw a o at right angles toa 0, meeting the vertical…
Architecture · Civil engineering · Science
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![An illustration from L'optique divisée en trois livres : ou, l'On démontre d'une maniere aisée tout ce qui regarde 1. la propagation & les proprietez de la lumiere. 2. La vision. 3. La figure & la disposition des verres qui servent à la perfefectionner [sic] (1682)](https://img.insideoutlibrary.com/img/200/ia-loptiquedivise00ango-341-38.webp)
