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 Strand."' 



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) 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 



T1.r-— 



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 the small cross 

 level, which was introduced by Mr. Gravatt. The advantage of the circular 

 level over the common form, is its peculiarity in at once showing the devia- 

 tion of the instrument from horizontality in both directions, instead of only 

 one. 



IJolore describing the next improvement, it may be proper to state, that 

 the clumsiness of the common level consists in its being at all dependent on 

 the setting of the legs. This arises from the circumstance of the ball and 

 socket motion (K) being controlled in its action by the parallel plate-screvv.s 

 of Sisson {DJ, the consequence of which is, that, in using tlie common level, 

 care must be taken to set the in.slrument very nearly level by the ctjr, so as 

 to be within the range of the parallel plate screws (DJ, otherwise it is impos- 

 sible to adjust the instrument. And although to the practical man, the 

 trouble attending this may be comparatively small, still he will admit that it 

 is one of the most irkscjme jiarts of the whole oj eration of levelling ; to say 

 nothing of the time that is lost m adjusting the instrument afterwards willi 

 the parallel jilate-screws. What appeared to be wanting was a molicm for 

 the preliminary, or rough-scllhg, intermediate in nicety between those of the 

 parallel plate-screws and of iho legs. In order to gain this end, a ball and 

 socket motion (F), having a clamp (N), is introduced in adilition to the hall 

 and socket (K), « hose action is limited by Sisson's parallel plate-screws (DJ ; 

 so that my improved level has two ball and socket movements. 



of Water and Waterworks. Dy Stephen Switzi 



ulB. 4to 



With the instrument thus improved, the observer is made quite independent 

 of the level of the ground where hi' sets the legs of his instrument, and may 

 |ilace them without regurd to the inclination of the telescope to the horizon. 

 Looking first to the circular level ((i), and releasing the clamii (N) of the 

 ball and socket (1'"}, he, with one hand, moves the head of the instrument 

 till the bubble is in the centre of the circle, an ojioration which is done almost 

 instantaneously." The socket-screw (N) is then clamiied, and the telescope 

 bubble (IIHJ is brought to iheabsohdc level by a tlight touch of the par.illtl 

 plate-screws (D). In this way the legs of the tripod never need to be moved 

 after the instrument has been placed on the ground, and the parallel plate- 

 screws have almost nothing to do— advantages which all w ho are accustomed 

 to levelling will fully appreciate. 



In levelling over mountainous districts, it very often happen.s that it ia 

 desirable to selecl a station where the ground ^is so rugged and precipitous 

 as to render it difficult, if not impossible, to find three points for the extre- 

 mities of the legs of the instrument to rest on, which shall be on such levels 

 as to bring the telescope within the range of the parallel plate-screws ; but 

 wherever the instrument can be made to stand with safety, the babble of the im^ 

 proved level can be adjusted, and adjusted in exactly the same time, and with fjr- 

 aetly the same ease, as ij the instrument were placed on level ground. 



Another advantage of these improvements is the removal of a great prac- 

 tical difficully which is often experienced on sloping ground. The instrument 

 being set and properly adjusted, the observer, on looking through tlie tele- 

 scon', may dl.scover that he is not within the range of the levelling stall'; in 

 oihcr words, he has chosen a station too liigh or too low to admit of his 

 seeing any part of the stalf within the field of the object-glass. The only 

 remedy for this is to chouse a new station w here the instrument must be 

 again set up and levelled, at a great expense of time and trouble. In order 

 to remedy this, it was my intention atone time to have fixed on the telescope 

 a French level, on the principle of the jdummet, in order speedily to discover 

 before making the adjustments, whether the intended station were within the 

 range of the staff' or not. But the instrument can be roughly set with so 

 much quickness by means of the additional ball and socket, that the French 

 plummet may be considered as being now scarcely necessary. 



In my letter to the Secretary of the Institution of Civil Engineers, I pointed 

 out the advantages which would result to the surveyor were the theodolite 

 provided with a second ball and socket motion ; but no opportunity of trying 

 this has as yet occurred. 



Edinburgh, 1844. 



8 lu the annexed plan the instrument 

 hubbleofthecirculurlevcKGjis in tho ei 

 tlie tube (H HJ correspond with the tile mi 



8 shown off tlie level, go tha 

 ntre of the clrele ; nor does l 

 ilea made on the ^Usa, 



neither the air- 

 he air-bubble In 



REGISTER OF NEW PATENTS. 



(Under tliis head we propose giving abstracts of the B])ecilicati(ina of all the most Ini. 

 portant patents as tliey are enrolled. If any additional information be required as to any 

 patent, the same may be obtained by applying to Mr. LAXTON at the OlBce of this 

 JOURNAL.) 



CONSTRUCTIO.V OF HARBOURS, &C. 



jAMtis Bremner, of Puultney Town, in the county of Caithness, civil engi- 

 neer, for *^ certain arrangements fur constructing harbours, inert and buildings 

 in water, far cleansing harbours and for raising sunken vessels." — Granted May 

 2'2, Enrolled Nov. 22, 1844. 



One part of the invention consists in certain arrrangemenis w hereby a wall 

 or other structure may be built near a quarry or other convenient spot, and 

 floated to a distance, and placed in the site in which it is to remain perma- 

 nently. For this purpose a floating structure or vessel is built in compart- 

 ments of two distinct kinds, wheicof one set is intended to contain the wall 

 and the other set to afford the buoyancy requisite for sustaining and floating 

 the wall or the other structure so as to admit of its being transferred from 

 ire place at which it is built to the place in which it is to be deposited. The 

 i ( of compartments for giving buoyancy or floatation to the vessel is gene- 

 rally arranged around the interior of the vessel, 30 as to suiround the com- 

 partments for containing the wall ; they may be of any convenient number 

 and size, each is to be furnished with the means of leltingin the water when 

 rcijuired, and at other times to be jierfectly water tight. The total aggregate 

 contents of the compartments of floatation, must be varied accordingly to the 

 weight of the wall or other structure which is to be transported, the princi- 

 ples upon which the leqnisitc sustaining power is to be obtained being well 

 understood by engineers. The compartment of the vessel containing the wall 

 or other structure has a moveal/e bottom, which during the building of the 

 wall and the floating of it out to the proposed site is sustained and kept close 

 to the vessel by chains, and caulked or rendered water tight by any of the 

 various metliods w ell kiionii to shipwrights; upon tlii.'i bottom, which is called 



