1820 July 10
Of purely curved lined [simple and regular] solids
Question 1. How many and what different
sorts of purely curved lined simple and regular
solids does the nature of things admit of?
Answer. Two sorts: viz spheres and spheroids.
Question 2. How may the figures of these several
solids be most commodiously described?
Answer. By showing in what manner they
may be formed.
Question 3. Show in what manner a sphere
may be formed?
Answer. Conceive a thing circular plate of
metal or other hard substance. Being circular,
it will have within the circumference a point
so situated that from it all lines that can be
drawn from it to the circumference will be
equal to one another. Such point is called the
centre of the circular. Any one such line, if continued
in the opposite direction till it reaches the
circumference, constitutes what is called the diameter
of the circle. Each half of this Diameter is
called sometimes a semi-diameter, sometimes a
radius of the circle. Considered in respect of the
use application now about to be made of it, it may be called
the axis of the circle. Conceive now the vessel considerably
larger than what was necessary to receive
this circular plate standing upon its axis as above:
conceive it filled with some compact but soft
and yielding substance capable of answering the
purpose of a mould: for example clay or bees-wax.
After having taken out a sufficient quantity of the
substance of this mould, conceive the circular plate
let into it with the axis in an upright situation and
turned round upon its axis till it has pushed away the
matter of the mould in such sort as to form a sort
of shell or cavity
within which the
circular plate turns
freely without finding
any portion of
the matter of the
mould in its way
to impede its course:
yet so as, at its circumference,
itself, during the whole
of its course, in contact
with every part
of it, in contact with
some part of the
matter of the mould
Identifier: | JB/135/261/001
"JB/" can not be assigned to a declared number type with value 135.
copy/fair copy sheet
c1 / g74
john flowerdew colls