The Artist's Assistant, In the Study and Practice of Mechanical Sciences: Calculated for the Improvement of Genius. Illustrated with Copper-Plates (Birmingham, [ca. 1785])

42 THE ARTIST'S ASSISTANT,

jection. 3. The reprefentation of a circle placed
obliquely to the eye, will be a circle in the plane
of projection. 4. If a great circle is to be projected
on the plane of another great circle, its center will
lie in the line of meafures, diftant from the center
of the primitive by the tangent of its elevation
above the plane of the primitive. 5. If a leffer cir-
cle, whofe poles lie in the plane of the projection,
were to be projected, the center of its reprefenta-
tion would lie in the line of meafures, diftant from
the center of the primitive, by the fecant of the
leffer circles diftance from its pole, and its femi-
diamcter or radius be equal to the tangent of that
diftance. 6. If a lefler circle were to be projected,
whofe poles lie not in the plane of the projection, its
diameter in the projection, if it falls on each fide
of the pole of the primitive, will be equal to
the fum of the half tangents of its greateft and
neareft diftance from the pole of the primitive, fet
each way from the center of the primitive in the
line of meafures. 7. If the leffer circle to be pro-
jected, falls entirely on one fide of the pole of pro-
jection, and does not encompafs it, then will all its
diameter be equal to the difference of the half tan-
gents of its greateft and neareft diftance from the
pole of the primitive, fet off from the center of the
primitive one, and the fame way m the line of
meafures. 8. In the ftereographic projection, the
angles made by the circles of the furface of the
fphere, are equal to the angles made by their re-
prefentation in the plane of their projection.

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