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SURVEYING- AND LEVELLING INSTRUMENTS—THEODOLITES, &c. [Class X.
transit axis are east in one piece, and to which is attacheda spirit level. The telescope is soldered to the axis, andthe vertical circle is firmly screwed to it, so that the ver-tical circle, axis, and telescope, are firmly connected.The whole instrument is formed of the smallest numberof pieces, with the view of preventing flexure and insuringstability. The Jury awarded Honourable Mention.
Joseph (Canada, No. 182, p. 908) exhibits a G-inchtheodolite of very indifferent workmanship.
Elliott and Sons (No. 320, p. 444) exhibit an altitudeand azimuth instrument of the ordinary construction. Itis understood that this instrument is intended chiefly forsurveying purposes; it is coarsely divided. They alsoexhibit two transit theodolites, the one of 5 inches andthe other G inches diameter. These instruments were notadjusted. Messrs. Elliott and Sons also exhibit dumpy-levels of good workmanship. In those exhibited, theindex-bar on which the level rests is placed vertically,instead of horizontally, as they were in those by Mr.Garratt, the inventor of this kind of level. There is alsoa change in the mode of adjusting the bubble; instead ofthe use of three screws at either end of the bubble, thereis one strong joint at one end, and a screw at the other;the joint cannot move till the screw at the other end isloose, and it is so constructed that it is almost impossibleto become loose by travelling; and they exhibit an instru-ment based upon the principle of similar triangles, adaptedfor the determination of distances.
Bridges (No. 339, p. 448) exhibits an instrument todetermine the distances of objects, either by night or byday, and rules are given to determine the distance whenthe height is known, or when its breadth is known, or whenneither is known, and also to determine the same by night.
Barton (No. 70S, p. 473*) has exhibited an instrumentdesigned for sketching ground, for military purposes, withgreat rapidity. It is designed with a view to its beingmanageable in the hands of men engaged in militaryservice, without regard to their scientific acquirements.Its simplicity of construction renders it very inexpensive.
For description of this instrument, see Illustrated Cata-logue. Honourable Mention is given to this exhibitor.
Liddell (No. 3G2, p. 450) has exhibited pocket-sightand field-sight spirit-levels to the number of 30, as used bymechanics, and adapted for drainage, road surveying, &c.
The spirit-levels are exhibited on account of lowness ofprice; some of the sight-levels are furnished with reversesights; there is one level with a revolving shade, intendedas a safeguard to the level tube.
Adcock (No. 353, p. 449) has exhibited a machine fordrawing and mapping roads.
Green (No. 446, p. 4G2) has exhibited a miner’s com-pass.
Cox (No. 347, p. 449) has exhibited a beam draininglevel, with adjusting parallel plates on tripod stand. It isa simple and inexpensive instrument, giving, by inspection,the rise and fall of land intended to be drained. It is alsouseful in laying tiles, levelling, and in building operations.Mr. Cox has also exhibited an A level, to be used withouteither parallel plates or tripod stand.
Blytii (No. 3G7, p. 450) exhibits four levels, of dif-ferent lengths, with stand and small telescope.
Doans (No. 346, p. 449) exhibits a spirit-level, appli-cable for levelling machinery.
Horxf, Thorntiiwaite, and Wood (No. 220, pp. 434,435) exhibit an angular spirit-level, showing the rise andfall in inches and parts. It is adapted for agriculturalpurposes.
Denton (No. 317, p. 443) exhibits a workman’s drain-ing A lewd, with a bob, intended for the use of farmlabourers; and a second level of the same constructionfurnished with a spirit-level.
Wilton (No. 402, p. 453) exhibits a miner’s tbeodolite.
Bcron (France, No. 443, p. 1199) exhibits a repeatingtheodolite with concentric circles, 8*7 inch diameter,divided to 10", and read by four verniers to 10". It isfurnished with two telescopes of 17*7 inches in length,and apertures 1*2 inch. The vertical circle is 4*3 inchesin diameter, and is divided to 30". Mr. Buron also ex-hibits several levelling instruments.
the form used by Gambey. Its circle is 13 inches indiameter, divided on silver to 10 centesimal minutes, readby means of four verniers to 10 seconds, and is adaptedto take either horizontal or vertical angles.
The azimuthal circle is 8*7 inches in diameter. It isdivided upon silver, and is read by a single vernier. Itis furnished with two levels. The telescope is 1*8 inchaperture, and 19 *3 inches focal length. There is a counter-poise attached, to be used when vertical angles are to betaken. This instrument was constructed for the Depotde la Guerre, in Belgium , for which service all the instru-ments are divided upon the centesimal system, but M.Beaulieu has likewise divided this instrument sexugesi-mally, the principal circle reading to 4 seconds of arc, andthe azimuthal circle to 20 seconds. All the divisions oftliis instrument are very good, as indeed is the workman-ship of the whole instrument, and the sextants exhibited(see Section, Nautical Instruments); a Prize Medal wasvoted to M. Beaulieu.
Groktaers (Belgium, No. 156, p. 1156) exhibits aninstrument for determining the distance of inaccessibleobjects. It is stated that the results obtained by tiie useof tliis instrument have been good.
De IIennallt (Belgium, No. 183, p. 1157) exhibits aminer’s compass, intended for use in determining the co-ordinates of a mine.
Lambert (Belgium, No. 185, p. 1157) exhibits a smallminer’s compass, but not so well made as the preceding.
Becker (Netherlands , No. 83, p. 1147) exhibits a level-ling apparatus.
Breitiiaupt (Prussia, No. 670, p. 1087) exhibits atheodolite. In this instrument, as in most theodolites ofGerman make, the circle which carries the verniers is letinto, and surrounded by, the graduated circle, so thattheir upper surface, on which the graduations are traced,are in one plane. In order to protect the divisions fromdirt, rain, and from mechanical injury, the vernier circlecarries a thin circular plate of brass, -which completelycovers the graduated or outer circle, with the exceptionof two openings, covered with plate glass, through whichthe verniers can be seen.
Tliis useful covering for the graduations, though nowused by other artists, was, we believe, first introduced byMr. Breitiiaupt.
Mr. Breitiiaupt also exhibits a level, which instead ofhaving circular collars on the telescope, which it is diffi-cult to make of equal diameter, and, if accurate when theinstrument is new, are very apt to bear unequally, hastowards each end of the telescope a knife-edge, and oppo-site to it, on the other side of the tube, a steel screw witha convex head; one knife-edge is on the upper side of thetube and one on the lower side. The level is attached toa plate of steel, having its under surface ground trulyplane. By turning the convex-headed screws, the planesthrough the knife-edges, and touching the heads of thescrews, can be made parallel to a line joining the centreof the object-glass and the intersection of the cross wires,and therefore to each other. The line of colimation ofthe telescope will be truly horizontal when the bubble ofthe level maintains the same position before and afterinversion. This contrivance greatly increases the facilityof adjusting a level, and of rendering the person using itindependent of the skill of the maker.
It is a common error among surveyors to assume thatthe circular collars of a level are of equal diameter ; andas long as tliis belief prevails, this invention must be ofpeculiar importance.
Mr. Breitiiaupt also exhibits a mining theodolite. Tliisinstrument is attached to its tripod by a slightly conicalsocket, and the graduated circle is made horizontal bytwo screws, opposed by two strong springs. The graduationof the horizontal circle is to 30" and has two verniers. Itsdiameter is nearly 4j- inches. The rertieal circle, whichis about the same diameter, is also read to 30'' by twoverniers.
The telescope, whose aperture is about 11 lines at theplace -where it meets the horizontal axis, lias a right-angled prism, which reflects the rays coming from theobject-glass. At one extremity of the long horizontalaxis are placed cross wires, adjustable by rack and pinion,