New Discovery in Oplics. 69 
to eranes, by which the labour of winches is performed by row- 
ing, &c.; on taking a view of the immense spirit vaults, he was 
forcibly struck by the inefficient mode adapted to light those very 
extensive and wonderful depéts*, which is by a cast-iron eylinder 
of about two feet in diameter, and two feet deep,placed in lieu of 
a key-stone in the centre of each arch ;—these cylinders are 
elosed at their tops, and each furnished with five plana-convex 
lenses (bull’s eyes) of Messrs. Pellatt and Green’s patent, which 
are admirably adapted to the conveying of light in all situations, 
except down a deep tube or cylinder, where the refraction they 
produce (in consequence of their convex form) betwixt the angles 
of incidence and reflection, prevents the rays from being pro- 
jected into the place intended to be lighted. This refraction 
throws the light upon the concave sides of the cylinder, where 
it is principally absorbed, instead of keeping the angles of inci- 
dence and reflection equal. — 3 
From these observations, Mr. Lester concluded, tiat a Jens 
might be so constructed as to prevent this refraction, and com- 
menced a course of experiments for that purpose. He succeeded 
by obtaining the proper angle of the incidental rays with a mirror, 
and finding the scope of the cylinder sufficiently copious to ad- 
mit the reflected rays into the vault, provided the refraction of 
the lens did not intervene. The same angle produced by the 
mirror he endeavoured to retain upon the sides of the lens, by 
giving ita different form, a peculiar part of which he intended 
to foliate. But having met with insurmountable difficulties in 
this process, he concluded, from the striking appearance of sil- 
very light upon the interior surface of that part he intended to 
silver, that metal would represent the light by retaining that 
form, and, brought down below the edges of the Iens, might 
produce the desired effect. In his attempt to accomplish this 
purpose, by holding the body in a vertical position between the 
eye and a candle, a flash of light was instantly produced, by re- 
presenting the flame of the candle magnified to the size of the 
whole of the inner surface of this piece of metal, and gave an in- 
creased light upon the wall opposite to him. After this disco- 
very, he had several pieces of metal formed, retaining the same 
angle, but of various diameters, and found to his great surprise, 
that, although their area were greatly increased, the representa- 
tion of the flame still filled them without the least diminution in 
the quality of the light, but with an increased light against the 
wall, in proportion to the: inereased area of the surface of the 
* One of which is nearly an acre and an half in area, and is swpported 
by 207 groined arches and 207 stone pillars. 
E 3 metal, 
