. The Civil engineer and architect's journal, scientific and railway gazette. Architecture; Civil engineering; Science. 1845.] THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 53 wa3 the inlroduction of tlio four screws called Ihc parallel plalc-srrrws (D, in tile Diagram). I liavc ln'cn unable to find out the date of Sisson's improve- ment; anil, indeed, the only notice I can find of him is the folluwinR in S« ilzi-r's System of Water-works : " The invention" (alluiling tci the instru- ment w)th parallel [ilatc-screws) " as I take it (for I am not as yet well ac- quainted with that
. The Civil engineer and architect's journal, scientific and railway gazette. Architecture; Civil engineering; Science. 1845.] THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 53 wa3 the inlroduction of tlio four screws called Ihc parallel plalc-srrrws (D, in tile Diagram). I liavc ln'cn unable to find out the date of Sisson's improve- ment; anil, indeed, the only notice I can find of him is the folluwinR in S« ilzi-r's System of Water-works : " The invention" (alluiling tci the instru- ment w)th parallel [ilatc-screws) " as I take it (for I am not as yet well ac- quainted with that sjentleman), of William Sisson, at the corner of Beaufort Buildings, in the ;' Since the time of Sisson, the cclehrated Ramsden introduced a tangent- screw and clamp, for moving the instrument with accuracy through small distances in an azimuthal direction. Messrs. Troiighton anil Simms also made several improvements in the arrangement of the various parls of the instrument; and Mr. Ciravatt has of late years added a cross-bubble for fa- cilitating the raHif/i-scZ/iny of the instrument—or that adjustment which is made with the legs of the tripod ; and an enlargement of the diameter of the object-glass, so as, by the admission of a greater number of rays of light, to allow of the telescoir being shortened, without impairing its optical powers. A D is the telescope.—C C the compass-box.—M the screw for adjusting the focus.—II II, the tubular spirit-level.—G, the spherical or circular level.— L) 0 D, the parallel plate-screws of .Sisson.—K, the old ball and socket mo- lion.—F, the new ball and socket motion.—N, clamping-screw for ditto. ,.-f —. Having thus endeavoured to describe the successive changes which the level has undergone, 1 shall now proceed to nolico the nature of the presen ' improvements. Tlie first of these is the substitution of a circular, or to speak more cor- rectly, a spherical level (G), sluggish in its motions, instead of
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