OPTICS. 
64S 
are thofe which have a curvilineal form, fuch as circles, 
ellipfes, looped curves like the figure 8-; curves like the 
figure 3 and the letter S; fpirals ; and other forms, fuch 
as. fquares, reftangies, and triangles, may be applied with 
advantage. Glafs, both fpun and twilled, and of all co¬ 
lours and (hades of colours, fhould be formed into the 
preceding (hapes ; and, when thefe are mixed with pieces 
of flat coloured glafs, blue vitriol, native fulphur, yellow 
orpiment, differently-coloured fluids enclofed and moving 
in fmall vefl'els of glafs, &c. they will make the fined trans¬ 
parent objefts for the kaleidofcope. When the objefts 
are to be laid upon a mirror-plate, fragments of opaquely- 
coloured glafs fhould be added to the tranfparent frag¬ 
ments, along with pieces of brafs wire, of coloured foils, 
and grains of fpelter. In (electing tranfparent objects, 
the greateft care mud be taken to rejeft fragments of 
opaque glafs, and dark colours that do not tranfmit much 
light; and all the pieces of fpun glafs, or coloured plates, 
fhould be as thin as poflible. 
When the objects are thus prepared, the next dep is to 
place them in the objeft-plates. The didance between 
the interior furfaces of the two plane glafles, of which the 
objeft-plates are compofed, fhould not exceed i-8th of 
an inch. The thicknefs of the tranfparent glafs next the 
reflectors fhould be juft fufficient to keep the glafs from 
breaking ; and the interior diameter of the brafs rings into 
which the tranfparent and the grey glafs are burnifhed, 
fhould be fo great, that no part of the brafs rim may be 
oppofite the angular part of the reflectors during the ro¬ 
tatory motion of the cejl. If this precaution is not at¬ 
tended to, the central part of the pattern, where the de¬ 
velopment of new forms is generally the mod beautiful, 
will be entirely obliterated by the interpolition of the 
brafs rim. When the two parts of the objeft-plate are 
fcrewed together, it fhould be nearly two-thirds filled 
with the mixture of regular and irregular objects, already 
mentioned. If they fall with difficulty during the rota¬ 
tion of the cell, two or three turns of the fcrew backward 
will relieve them ; and, if they fall too eafily, and accumu¬ 
late, by flipping behind one another, the Apace between 
the glafles may be diminiflied, by placing another glafs in 
contaft with the grey glafs. 
When the objeft-plate, now' defcribed, is placed in the 
cell, and examined by the kaleidofcope, the pictures 
which it forms are in a date of perpetual change, and can 
never be fixed, and fliown to another perfon. To obviate 
this di fad vantage, an objeft-plate with fixed objefts ge¬ 
nerally accompanies-theinftrument; the pieces of fpun and 
coloured glafs are fixed by a tranfparent cement to the 
inner fide of the glafs of the objeft-plate, next the eye, fo 
that the patterns are all permanent, and may be exhibited 
to others. After the cell has performed a complete rota¬ 
tion, the fame patterns again recur, and may therefore be 
?.t any time recalled at the pleafure of the obferver. The 
fame patterns, it is true, will have a different appearance, 
if the light falls in a different manner upon the objefts; 
but its general character and outline will remain the fame. 
.The objeCt-plates, which have now been defcribed, are 
made to fit the cell, but at the fame time to flip eafily into 
it, fo that they themfelves have no motion feparate from 
that of the cell. An objeft-plate, however, of a lefs dia¬ 
meter, called the vibrating objeft-plate, and containing 
loofe objeCls, is an intereding addition to the indrument. 
When the kaleidofcope is held horizontally, this fmall 
-objeCt-plate vibrates on its low'er edge, either by.a gentle 
motion of the tube, or by ftriking it (lightly with the 
finger; and the effeCt of this vibration is Angularly fine, 
particularly when it is combined with the motion of the 
coloured fragments. 
Another of the objeCt-plates, in feveral of the inflru- 
•mer.ts, contains either fragments of colourlefs glafs, or 
an irregular furface of tranfparent varnifh, or indurated 
.Canada balfam. This objeft-plate gives very fine colour¬ 
lefs figures when ufed alone; but its principal ufe is to 
,be placed in the cell between an objeft-plate with bright 
colours and the end of the inftrument. When this 13 
done,, the outline of the pieces of coloured glafs are I of¬ 
ten ed -down by the refraftion of the tranfparentfragments, 
and the pattern difplays the fined effefts of loft and bril¬ 
liant colouring. The colourlefs objeft-plate ('applies the 
outline of the pattern, and the mafs of colour behind 
fills it up with the fofteft tints. 
Some of the objed-plates are filled with iron or brafs 
wdres, twifted into various forms, and rendered broader 
and flatter in fome places by hammering. Thefe wires, 
when intermixed with a few fmall fragments of coloured 
glafs, produce a very fine effeft. Other objeft-plates 
have been made with pitch, balfam of tolu, gum lac, and 
thick tranfparent paints; and, when thefe fubftances are 
laid on with judgment, they form excellent objefts for 
the kaleidofcope. Lace may be introduced with confi- 
derable efreft, and alfo feitoons of beads ftrung upon 
wire or thread ; but pieces of glafs, with cut and poli(hed 
faces, are entirely unfit for objefts. 
Compound or Telefcppic Kaleidofcope. —We have already 
feen, in explaining the principles of the kaleidofcope, 
that a fymmetrical pifture cannot be formed from objefts 
placed at any diftance from the inftrument. If we take 
the Ample kaleidofcope, and, holding an objeft-plate in 
contaft with the refleftors, gradually withdraw it to a 
diftance, the pifture, which is at firil perfeft in evefy part, 
will, at the diftance of i-ioth of an inch, begin to be dis¬ 
torted at the centre, from the difunion of the reflefted 
images; the didortion will gradually extend itfelf to the 
circumference, and at the diftance of eighteen inches, or 
lefs, from the refleftors, all the fynrmetry and beauty of 
the pattern will difappear. An unexperienced eye may 
(till admire the circular arrangement of the imperfeft and 
diflimilar images; but no perlon acquainted with the in¬ 
ftrument could endure the defefts of the pifture, even 
when the flighteft diftortion only is vifible at the centre. 
As the power of the kaleidofcope, therefore, in its Ample 
form, is limited to tranfparent objefts, or to the outline 
of opaque objefts held dole to the aperture of the reflec¬ 
tors, it becomes a matter of confequence to extend its 
power, by enabling it to produce perfeftly-fymmetrical 
patterns from opaque objefts, from immovable objefts at 
a diftance, or from objefts of fuch a magnitude that they 
cannot be introduced before the opening of the refleftors. 
Without fuch an extenlion of its power, the kaleidofcope 
could only be regarded as an inftrument of amufement; 
but, when it is made to embrace objefts of all magnitudes, 
and at all diltances, it takes its place as a general philo- 
fophical inftrument, and becomes of the greateft ufe in 
the fine, as well as the ufeful, arts. 
“ In confidering how this change might be effefted, 
(fays Dr. B.) it occurred to me, that if MN, fig. 13, were 
a diftant objeft, either opaque or tranfparent, it might be 
introduced into the pifture by placing a lens, LL, at fuch 
a diftance before the aperture AOB,that its image may be 
diftinctly formed upon the plane palling through AOB. 
By fubmitting this idea to experiment, I found it to an- 
fwer my mod (anguine expectations. The image formed 
by the lens at AOB became a new objeft, as it were, and 
was multiplied and arranged by fuccefiive reflections in 
the very fame manner as if the objeft MN had been re¬ 
duced in the ratio ML to LA, and placed clofe to the 
aperture.” 
The compound kaleidofcope is therefore fitted up as 
fliown in fig. 14, with two tubes AB, CD. The inner 
tube, AB, contains the refleftors, (as in fig. 11.) and at 
the extremity C, of the outer tube CA, is placed a lens, 
which may be taken off, or put 011, at pleafure. The focal 
length of this lens fhould always be much lefs than the 
length of the outer tube CA, and fhould in general be 
fuch, that it is capable of forming an image at the end of 
the refleftors, when AB is pulled out as much as poflible, 
and when the objeft is within three or four inches of the 
lens. When it is required to introduce into the pifture 
very large objefts placed near the lens, another lens of a lefs 
focal 
