Class X.]

CRYSTALLOGRAPHY—DRAWING INSTRUMENTS.

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famished with a ehronometrie controller. It consists oftwo levers fixed to an iron frame, which mutually act oneach other by a joint; to one of these the plough isattached, and to the other a counterpoise which consti-tutes one of the factors for the measurement of power, asit changes its position with a change of strain, whichchanges are marked as the lever moves.

The ehronometrie controller consists of two watchesprovided with seconds-hands, one of which is unalfected bythe pull, and merely indicates ordinary time, whilst theother is acted upon by the varying position of the lever,in such a manner tliat its rate per minute varies with thevarying strain, and is self-registered. By this means allvarying resistance is recorded, such as is experienced inthe towing of a ship, &c., cases in which the ordinarydynamometer acted upon by means of a spring, is foundto fail.

Crystallography.

Leeson (Class I., No. 8, pp. 120, 121,) exhibits a verybeautiful collection of crystals; the apparatus for illus-trating the crystallographic speculations published byDr. Leeson, in the third volume of the Memoirs of theChemical Society; a double-refracting goniometer: andnumerous models of crystals. A Prize Medal was awardedto Mr. Leeson.

It is difficult to understand why the remark “ rectan-gular” is annexed to a model labelled antimony. Foraccording to the independent observations of Marx,G. Rose, M. Zippe, and llaidinger, antimony crystallizesfrom fusion in a form, the faces of which make, with eachother, angles differing nearly two and a half degrees froma right angle.

Mitchell (Class I., No. 9, p. 121) exhibits a collectionof crystals: some very beautiful card-board models ofcrystals, in which the faces of each have a distinctivecolour, as in some of the plates of Tennant’s Mineralogy ,and are marked with symbols according to the notationadopted by different crystallographers.

Also some very ingeniously contrived skeleton models,showing the outline of all the simple forms of a crystal-line species, referred to the same axis.

Other models, some to illustrate theoretical views, areexhibited by Mr. Mitchell, according to which, the simpleforms of crystals of any system may be derived from thoseof a crystal of the cubic or octahedral system. A PrizeMedal was awarded to Mr. Mitchell.

Luhmk : Prussia , No. 83, p. 1053) exhibits an extremelygood collection of models of crystals, selected byG. Rose.

Schroder (Grand Duchy of Hesse, No. 77, p. 1129,)exhibits models of crystals, described in Kopp’s “ Einlei-tung in die Krystallographie,” on a large scale, which areprobably the best-executed models that have yet beenmade: he also exhibits various models of geometric solids,which appear to be as well executed as the crystals. APrize Medal was awarded by the Jury to ProfessorSchroder.

Batka (Austria, No. 135, p. 1014) exhibits some verygood models of crystals in glass.

Bkrtaud (France, No. 1549, p. 1251,) exhibits modelsof crystals.

Drawing Instruments.

Varley and Son (No. 257, p. 436) have exhibited agraphic telescope and table; also a small graphic stand,adapted for use on an ordinary table.

The telescope is furnished with a variety of powers,and affords every variation of size in the object to betraced, which may be sketched to the true perspectivedistance of the picture on which it is to be placed.

The field of view is large, but the picture may beextended by moving the telescope, and shifting the paper,there being a means of applying correction, if necessary.

The paper or drawing surface may be placed in anyconvenient direction, and inclined at any angle, the in-strument affording facilities for delineating objects in allpositions, whether overhead, on the floor, or right and left.The image can be adjusted with equal precision at whatdistance soever the eye may be removed from the paper,and may also be reversed, for lithograpliic purposes.

| This instrument has assisted in the production of theI great “ Panorama of London, as seen from the top of St.Paul's,” at the Colosseum , in the Regent’s Park, and inthat of Corfu , the coloured sketches for which, on a largescale, were made by the late Joseph Cartwright, Esq.

The graphic telescope is designed to afford assis ance toartists, architects, and draftsmen, by presenting to theeye a correct image of the object to be traced, in anydirection and of any size required.

In order to trace telescopic images, great steadiness andportability are required. Both these requisites appear tobe combiued in the graphic table exhibited by Mr. Varley.The framework is so constructed as to be extremely lightand steady; the joinings are made with hinges, fromwhich the pins may be removed, and the instrumentpacked into a small compass. The table itself is sup-ported upon a braced tripod, and admits of adjustmentupon any surface, however irregular; it can also be sup-ported at any angle.

Elliott and Sons (No. 320, pp. 443, 444) exhibit afine magazine ease of drawing instruments, inclusive ofall the recent improvements; the two trays with which itis furnished, and the interior of the lid contain metalrulers, sectors, triangles, ivory sectors, parallel ruins,pocket rules, a graduated joint for taking augles, Sec.The metal sectors are well divided, as are also those madeof ivory. In the drawers is a complete set of watercolours. This set of instruments, the case of which is initself a fine piece of workmanship, was rewarded with aPrize Medal.

The same exhibitors have another case of instruments,of good workmanship, and highly ornamented by engrav-ing and chasing. They exhibit also various sets of ivorysectors, divided from 10 to 100 to the inch, and ivoryparallel sectors, capable of being used on both sides, withdivided edges both sides. They also exhibit a small in-strument called an opisoineter, intended fo- measuring thelength of curve lines. It consists of a small roller, which,having beeu passed over the lines, is made to perform thesame number of revolutions over a scale.

Pillischer (No. 269, p. 437) has exhibited an ellipto-graph. The principle upon which this elegant littleinstrument is made to describe an ellipse, is that of a pointrevolving in a circle about a centre, with an angular velo-city the double of that with which the centre revolvesabout a fixed centre. The cogs on a moveable bar, andwheels of the instrument are so arranged that the shortann which holds the style performs lot) revolutions whilethe long a itu performs one. By varying the relativelengths of the two arms an ellipse of any form may bedrawn. The semi-major axis of the ellipse will be mani-festly equal to the sum of the two radii or amis, and theminor axis equal to their difference. A Prize Medal wasawarded to Mr. Pillischer.

Simms (No. 741, p. 475*) exhibits an isometrical ellipto-graph. Invented by G. B. Airy , Esq., the AstronomerRoyal.

Dobson (No. 323, p. 446) has exhibited many well-madesets of drawing instruments, so far as could be seen throughthe glass case, which was never opened for the examina-tion of the Jury.

Tree and Co. (No. 324, p. 446) have exhibited somewell-made drawing instruments, with many accuratelydivided scales for different purposes. The Jury awardedHonourable Mention.

Parke and Sons (No. 337, p. 448) have exhibited well-made drawing instruments, and several well-divided scales.

Dixey (No. 271, p. 43$) has exhibited several mathe-matical instruments, amongst which is a divided ivoryrolling parallel rule.

Haggard (No. 328, p. 446) exhibits a double pro-tractor, intended for measuring angles, and determiningheights and distances.

Graham (No. 355, p. 449) exhibits an ivory rule, onefoot in length, and an inch and a half in breadth, for thepurpose of exhibiting by inspection the circumference of acircle when the diameter is given, and vice versa , and forshowing the side of the square equal in area to that of acircle, whose diameter or circumference is given.

One side of the rule contains three lines extending its