650 OPT 
fcrewed. Thefe two cones enclofe two liighly-poliflied 
metallic reflectors AO, BO, fig. 17. only one of them, 
viz. BOE, being feen in fig. 16. One of thefe reflectors, 
BOE, is fixed to the ring RR, by the intermediate piece 
KGL. The reflector is fcrewed to this piece by the ad- 
juftable fcrews K, L; and the piece KGL is again fixed 
to the ring RR, by two fcrews feen above and below G, 
in fig. 17. Hence the tube, confifting of the cones MM, 
NN, and the ring RR, fig. 16, are immovably connected 
with the mirror BOE. The furface of the reflector BOE 
is adjufted by the fcrews at K and L, till it pafles accu¬ 
rately through the axis of the cones and ring, as feen in 
fig. 17. The other refleCtor, AO, is fixed to an outer 
ring rr, by means of an intermediate piece, fimilar to 
KGL, the arm F of which, correfponding to G, pafles 
through an annular fpace, or open arch, of more than 90 0 , 
cut out of the circumference of the inner ring RR. The 
arm F is fixed to the outer ringrr by two fcrews, feen above 
and below' F, in fig. 17, and the refleCtor AO is fixed to 
the bar correfponding to KL by fimilar fcrews, for the 
purpofe of adjufting it. The low'er edge OE of the re¬ 
flector BOE extends about the fifteenth of an inch below 
the axis of the cones, as reprefented by the dotted line in 
fig. 16. but the lower edge OF, of the other refleCtor AOE, 
which is finely ground to an acute angle, forming a per¬ 
fectly ftraight and fmooth line, is placed exaCtly in the 
axis of the cones, fo as juft to touch a line in the reflector 
AOE, which coincides w'ith the axis of the cones, and to 
form a junction with that line in every part of the two 
meeting planes. The very nice adjuftments which are 
necefi’ary to produce fo exaCt a motion are effected by the 
fcrews correfponding to K and L. 
If we now fix the outer ring rr into the ring of the 
Hand ST, fo as to be held faft, and turn the cones with 
the hand, we (hall give motion to the refledtor BO, fo as 
to place it at any angle we pleafe, from o° to 90 0 ; and, 
during its motion through this r arch, the junction of the 
tw'o refleCtors mull remain perfect, if the touching-lines 
are adjufted, as we have defcribed them, to the axis of 
motion, which muft alfo be the axis of the cones and 
rings. If, on the contrary, we take aw'ay the ftand, and, 
holding the inftrument in the hand by either of the cones 
M, N, turn the ring R with the other, we (hall give mo¬ 
tion to its refledtor AO, and produce a variation in the 
angle in the fame manner as before ; or the fame effeCt 
may be produced by an endlefs fcrew working in teeth 
cut upon the circumference of the outer ring rr. 
In order to enable the obferver to fet the refleCtors at 
once to any even aliquot part of a circle, or fo as to give 
any number of pairs of direCt and inverted images, the 
moft convenient of the even aliquot parts of the circle are 
engraven upon the ring rr, (though not exprefied in the 
plate;) fo that we have only to let the index to any of 
thefe parts, to No. 12. for example, and the refleCtors will 
then be placed at an angle of 30 0 , and will form a circular 
field with twelve luminous feCtors, or a ftar with fix points, 
and confequently a pattern compofed of fix pairs of direCt 
and inverted images. 
As the length of the plates is only about five inches, it 
is necelfary, excepting for perfons very lliort-fighted, to 
have a convex lens placed at E. A brafs ring containing 
a plane glafs fcrews into the outer ring, CD, when the 
inftrument is not in ufe ; and there is an objeCt-plate, con¬ 
taining fragments of differently-coloured glafs. This 
objeCt-plate coniifts of two plates of glafs, one ground 
and the other tranfparent, fet in brafs rims. The tranf- 
parent one goes neareft the refleCtor, and the brafs rim 
which contains it fcrews into the other, fo as to enclofe 
between them the coloured fragments, and regular figures 
of coloured and twifted glafs. A loole ring furrounds 
this objeCt-plate ; and, when this ring is fcrewed into the 
circular rim CD, the objeCt-plate can be turned round, fo 
as to produce a variety of patterns, without any rifle of its 
being detached from the outer cone. 
In applying this inftrument to opaque objeCts, fuch as 
ICS. 
engravings, coins, gems, or fragments of coloured glafs 
laid upon a mirror, the aperture of the mirrors is laid di- 
reCtly over them, the large cone MM having been pre- 
vioufly unferewed, for the purpofe of allowing the light 
to fall freely upon the objeCts. This property of the ka- 
leidofcope is of great importance, as in every other form 
of the inftrument opaque objeCts muft be held obliquely, 
and therefore at fuch a diftance from the refleCtors as muft 
affeCt the fymmetry of the pattern. 
As the perfection of the figures depends on the refleCtors 
being kept completely free from dull, particularly at the 
angles, where it naturally accumulates, the greateft faci¬ 
lity is given by the preceding conftruCtion in keeping 
them clean. For this purpofe, the large cone muft be 
unferewed ; the refleCtors having been previoufly clofed, 
by turning the index to 60 on the ring. They are next 
to be opened to the utmoft, and the dull may in general 
be removed by means of a fine point wrapped in clean 
and dry wafti leather. If any duft, however, Hill adheres, 
the finall fcre w in the fide of the ring oppofite to the index 
fliould be removed,and the (mailer cone NN alfo unferewed. 
By eafing the fupporting fcrews of either of the refleCtors, 
their touching (ides will feparate, fo as to allow a piece 
of dry wafli-leather to be drawn between them. When 
every particle of duft has been thus removed, the metals 
fliould be re-adjufted and clofed before the cones are re¬ 
placed ; both of which fliould be fcrewed firmly into the 
ring RR. 
Microfcopic Kaleulofcopes .—This name may be given to 
the inftrument under two forms; namely, when it is made 
to produce fymmetrical patterns from microfcopic objeCts, 
or when it is made fo (liort that a lens of a high power is 
necelfary at one end of the refleCtors, to fee diftinCtly, and 
magnify the objeCts at the otherend. I11 both thefe forms 
the inventor has often conftruCted them fo fmall as one 
inch and one inch and a half in length. As the kaleido- 
fcope, in this minute ftate, has been applied both in this 
country and abroad, as a female ornament, we fhall pro¬ 
ceed to point out the belt method of conltruCting it. 
Since the aberration from fymmetry increafes as the 
length of the refleCtors is diminiftied, and fince the light of 
the field diminiflies from the fame caufe,it becomes extreme¬ 
ly difficult toobtain correct figures and uniformity of light 
in fmall inftruments. In order to overcome thefe difficul¬ 
ties as far as poflible, the refleCtors fliould be metallic, 
and may be either made of poliihed fteel or poliflied fpg- 
culum metal. The inclination at which they are fixed 
fliould not be lefs than 36° or 45 0 ; and the eye-hole, 
which fliould not exceed i-i5th of an inch in diameter, 
muft be placed as near as poflible to the angular point. 
Since the aberration from fymmetry increafes with the dif- 
tance of the object from the refleCtors, and is much aug¬ 
mented in fmall inftruments, the greateft care muft be ta¬ 
ken to have the objeCts at the leaft poflible diftance from 
the reflectors. To accomplifli this, the objeCts themfelves 
fliould be as thin and (lender as they can be made ; the 
colours fliould be brilliant and not gloomy; and they 
fliould be feparated from the refleCtors by a thin film of 
the moft tranfparent mica, which is fuperior to glafs of 
equal thicknefs, even if it could be got, from its extreme 
toughnefs and elafticity. The mica, indeed, is ealily 
fcratched; but, if this fliould take place to any extent, it 
can eafily be replaced by a new film. It would even be of 
confequence to bend the mica into a flight concavity, fo 
as to permit the objeCts to lie rather within than without 
the extremity of the refleCtors. In order to fee the pat¬ 
tern with perfect diftinCtnefs, a lens muft be placed at the 
end of the inftrument: the focal length of this lens, 
however, muft not be exaCtly equal to the diftance of the 
objeCts from the eye, but as much greater as poflible, fo 
that the eye, by a little exertion, may be able to obtain 
diltinCt vilion. The reafon of this will be underftood, by 
confidering that the images of the objeCts, feen by reflec¬ 
tions, are thrown to a greater diftance, as it were, from 
the eye, and could not therefore be feen diftinCtly by ufing 
1 a lens 
