647 
OPTICS. 
be brought as near as pofiibie to E. When the plates 
have the fame breadth at both ends, the angular point E 
■will be near the lower circumference of the tube, as it is 
at O ; and, in this ca(e, it is necefiary to place the eye-hole 
out of the centre, fo as to be a little above the angular 
point E. This conftrufition is lefs elegant than the pre¬ 
ceding ; but it has the advantage of giving more room 
for the introduction of a feather, or a piece of thin wood 
covered with leather, for the purpofe of removing the 
duft which is conftantly accumulating between the re- 
fieCtors. In fome inftanees, the plates have been put 
together in fuch a manner, that they may be taken out 
of the tube for the purpofe of being cleaned ; but, though 
this conftruClion has its advantages, yet it requires fome 
ingenuity to replace the refleflors with facility, and to 
fix them at the exaCt inclination which is required. One 
of the molt convenient methods is to fupport the reflector 
in a groove, cut out of a folk! cylinder of dry wood, of 
nearly the fame diameter as the interior diameter of the 
tube ; and, aft'er a flip of wood, or any other fubftance, is 
placed along the open edges of the plates,- to keep them 
at the proper angle given by the groove, the whole is 
flipped into the tube, where it remains firm and fecure 
from all accident. If the length of the reflectors is lefs 
than the fhorteft diftancC at which the eye is capable of 
feeing objeCts with perfeCt diftinctnefs, it will be necefiary 
to place at the eye-end E a convex lens, whofe focal length 
is equal to, or an inch or two greater titan, the length of 
the refleflors. By this means the obferver veil! fee with 
perfeft diftinctnefs the objeCts placed at the objeCt-end of 
the kaleidofcope. This lens, however, mult be removed 
when the inftrument is to be ufed by perfons who are 
fhort-fighted. 
The proper application of the objeCts at the end of the 
refieCtors is now the only ftep which is required to com¬ 
plete the Ample kaleidofcope. The firft and molt Ample 
method confilts in bringing the tube about half an inch 
beyond the ends of the refleflors. A plane lens, of the 
fame diameter as the tube, is then pulhed into the tube, 
fo as to touch the reflectors. The pieces of coloured 
glafs being laid upon this lens, another plane lens, having 
its upper furface ground with fine emery, is next placed 
above the glafs fragments, being prevented from prefling 
upon them,' or approaching to the firft plane lens, by a 
ring of copper or brafs; and is kept in its place by bur- 
nifliing down theend of the tube. The eye being placed 
at the other end of the inftrument, the obferver turns the 
whole round in his hand, and perceives an infinite variety 
of beautiful figures and patterns, in confequence of the 
fucceflion of new fragments, which are brought oppofite 
the aperture by their own gravity, ajjd by the rotatory mo¬ 
tion of the tube. In this rude ftate, however, the inftru¬ 
ment is by no means fufceptible of affording very plealing 
exhibitions. A difagreeable- effect is produced by bring¬ 
ing the darkeft feffors, or thofe formed by the great- 
eft number of reflections, to the upper part of the circular 
field ; and, though the variety of patterns will be very great, 
yet the inftrument is limited to the fame feries of frag¬ 
ments, and cannot be applied to the numerous objects 
which are perpetually prefenting themfelves to our no¬ 
tice. Thefe evils can be removed only by adopting the 
conftruClion fliown in fig. n. in which the refleflors reach 
the very end of the tube. Upon the end of the tube ab, 
cd, fig. ia. is placed a ring of brafs, mn, which moves 
eafily upon the tube abed, and is kept in its place by a 
ftioulder of brafs on each fide of it. A brafs cell, MN, 
is then made to flip tightly upon the movable ring mn, lo 
that, when the cell is turned round by means of the milled 
end at MN, the ring mn may move freely upon the tube. 
The fragments of coloured glafs, &c. are-now placed in a 
fmall box, or objed-plate as it may be called, conflfting of 
two glafles, one tranfparent and the other ground, kept 
at the diftance of i-8th or x-ioth of an inch by a brafs 
rim. This brafs rim generally confifts of two pieces, 
which ferew into one another, lb that the objeft-plate can 
z 
be opened by unferewing It, and the fragments changed 
at pleafure. This objeCt-plate is placed at the bottom of 
the cell MN, as (hown at OP ; and the depth of the cell is 
fuch as to allow the fide O to touch the end of the reflect¬ 
ors, when the cell is flipped upon the ring mn. When 
this is done, the inftrument, fig. n. is held in one hand 
with the angular point E downwards, which is known by 
a mark on the upper fide of the tube between « and b, 
and the cell is turned round with the other, fo as to pre- 
fent different fragments of the included glafs before the 
aperture AOB. The tube maybe directed to the bright- 
eft part of the ftcy in the day-time, or in the evening to a 
candle, or an Argand lamp, fo as to tranfmit the light 
direCtly through the coloured fragments ; but it will 
always be found to give richer and more brilliant efteCts 
if the tube is directed to the window-ftiutter, a little to 
one fide of the light; or is heldfto one fide of the candle ; 
or, what is ftill better, between two candles or lamps 
placed as near each -other as pofiibie. In this way the 
picture, created by the inftrument, is not cotnpofed of the 
harfli tints formed by tranfmitted light, but of the va¬ 
rious reflected and loftened colours which are thrown 
into the tube from the fides and angles of the glafs frag¬ 
ments. 
In the preceding method of applying the objeCts to the 
reflectors, the fragments of coloured glafs are introduced 
before the aperture, and pafs acrofs it in concentric cir¬ 
cles ; and, as the fragments always defeend by their own 
gravity, the changes of the picture, though infinite in 
number, conftantly take place in a fimilar manner. This 
defeCt may be remedied, and a great degree of variety ex¬ 
hibited in the motion of the fragments, by making the 
objeCt-plates rectangular inftead of circular, and moving 
them through a groove cut in the cell at MN, in the 
fame manner as is done with the pictures or Aiders for 
the magic lantern ajad folar microfcope. By tiiis means, 
the different fragments that prefent themfelves to the 
aperture may be made to pafs acrofs it in every pofiibie 
direction, and very interefting effects may be produced 
by a combination of the rotatory and rectilineal motions 
of the objeCt-plate. 
When the Ample kaleidofcope is applied to opaque 
objefts, fuch as a feal, a watch-chain, the feconds-hand 
of a watch, coins, pictures, gems, (hells, flowers, leaves, 
and petals of plants, imprefiions from feals, &c. the ob- 
jeit, inftead of being held between the eye and the light, 
muft be viewed in the fame manner as we view objeCts 
through a~ microfcope, being always placed as near the 
inftrument as poflible, and to as to allow the light to fall 
freely upon the objeCt. The o'pject-plates, and all tranf¬ 
parent objeCts, may be viewed in this manner; but tbs 
molt fplerfidid exhibition of this kind is to view minute 
fragments of coloured glafs, and objects with opaque 
colours, &c. placed in a flat box, the bottom of which is 
made of mirror-glafs. The light reflected from the inir- 
ror-glafs, and tranfmitted through the tranfparent frag¬ 
ments, is combined with the light reflected both from the 
tranfparent and opaque fragments, and forms an effect of 
the fineft kind. 
Although the kaleidofcope is capable of creating beau¬ 
tiful forms from the raoft ugly and fliapelefs objects, yet 
the combinations which itprefents, when obtained from 
certain forms and colours, are fo fuperior to thofe which 
it produces from others, that no idea can be formed of 
the power and effedts of the inftrument, unlefs the objeCts 
are judicioufly feleCted. 
When the inclination of the refieCtors is great, the ob¬ 
jects, or the fragments of coloured glafs, fhould be larger 
than when the inclination is fmall; for, when fmall frag¬ 
ments are prefented before a large aperture, the pattern 
which is created has alpotted appearance, and derives no 
beauty from the inverfion of the images, in confequence 
of the outline of each feparate fragment not joining with 
the inverted image of it. 
The objeCts which give the fineft outlines by inverfion, 
are 
