sriRKix. 



SHRIT-LK\ 1. 1.. 



718 



Salisbury and Norwich, the spire u raised upon a tower at the inter- 

 section of the cron, or in the centre of the plan ; whereas in most 

 continental cathedral* and large churches there are two spires on the 

 tower* of the weet front, though in some instance* (Strasburg, Ant- 

 werp) only one has been erected. Several, however, have a single 

 tower and spire in the centre of the west front (Ulm, Kreyburg, Tlmnn 

 in Alsace), in which case the tower itself begins to diminish almost 

 from the ground, and the whole becomes what we have described as 

 of the tabtntadt character. In most of our English churches (not 

 cathedrals) the spire is placed upon a tower at the west end, as at 

 Umnthain, Louth, Bloxhiun, &c. If we except Peterborough, where they 

 ore very diminutive, the only English cathedral which has two western 

 spires is Lichfield, which is further remarkable as having a central 

 t. . i r and spire also. Betides the richness and variety thus produced, 

 the larger central spire serves to balance the whole composition, 

 whereas else the body of the structure is apt to look low in comparison 

 with the west end. At St. Stephen's, Vienna, the tower and spire are 

 singularly placed on the south Bide of the edifice, it having been 

 intended to balance them by a corresponding tower on the north 

 side. At Qeluhaiuen, on the contrary, there is a group of spires at the 

 east end. 



Though so much depends upon the proportion of spires to their own 

 diameters and to the height of the towers, almost the only thing that 

 is specified in the usual description of spires is the entire altitude from 

 the ground, which single measurement, unaccompanied by others, gives 

 no idea of the relative dimensions of the spire or how it is proportioned. 

 Some of the loftiest spires, as they are popularly termed, are by no 

 means lofty, being not above a third of the entire height, and not more 

 than four of their own diameters. The spire of Strasburg, for 

 instance, is only 110 feet out of 474, or less than one-third of the tower 

 itself. At Antwerp again the spire is a mere ptat crowning the upper- 

 most stage of the tower, while the tower itself in twice as high as the 

 roof of the church. If we compare Salisbury with Norwich, the spire 

 of the latter cathedral will be found, though of less dimensions, much 

 loftier in relation to the rest than the other, being in the ratio of 163 

 to 308 feet, while Salisbury is only 197 to 404. We have, therefore, 

 drawn up a short table of spires (see preceding page) showing, 

 where we can, the separate as well as united heights of the respective 

 towers and spires. 



SPIREIN. (C.jHj.O,,?) The yellow colouring matter of the 

 meadow-sweet (Spinea nlmtria). It is a crystalline yellow powder 

 insoluble in water, but very soluble in alcohol and ether. The dilute 

 solution is yellow, but becomes dark green on concentration. It 

 possesses a slight acid reaction, and cannot be volatilised, without 

 decomposition. 



st'ltUN. [SALICYLIC GROUP.] 



Sl'IUIT, a term used in chemistry. AVhen employed alone, it is 

 now almost exclusively applied to spirit of wine, or alcohol ; formerly 

 however the name spirit was given to most substances capable of being 

 vaporised and condensed by distillation, and to some not obtained by 

 .iist illation. It will be requisite merely to name a few of thoae com- 

 pounds to show how extensively it was used in naming substances of 

 very different origin and composition : thus nitric acid was called 

 spirit of nitre : hydrochloric acid, spirit of salt ; sulphuric acid, spirit 

 of sulphur ; chloride of tin, spirit of Libavius ; solution of ammonia, 

 spirit of sal-ammoniac, or sometimes spirit of hartshorn. 



SPIRIT-LEVEL, a tube of gloss nearly filled with spirit of wine or 

 distilled water, and hermetically sealed at both ends, so that when 

 held with its axis in a horizontal position, the air which occupies a part 

 not filled with the spirit or water places itself contiguously to the 

 upper surface. The tube being supposed to be perfectly cylindrical, 

 the exact horizontally of its axis is ascertained by the extremities of 

 the air-bubble being at equal distances from the middle point in the 

 length of the gloss. 



The spirit-tube is used in determining the relative heights of ground 

 at two or more stations, and in order to render it available for this pur- 



pose, it is placed within a brass case having a long opening on the side 

 which is to be uppermost, and U attached to a telescope ; the telescope 



and tube are then fitted to a frame, or cradle, of brass, which is sup- 

 ported on three leg*. In the interior of the telescope, at the common 

 focus of the object-glad and eye-gUnes, are fixed, generally, two wires, 

 at right angles to each other, their intersection being in the line of 

 collimation, or that which joins the "centre* of all the lenses. 



The case containing the spirit-tube is made to turn on a joint at one 

 extremity, as a, by the revolutions of a screw, 6, at the opposite extre- 

 mity ; and the telescope rests, near each end, within two arms at the 

 top of a small pillar, A or n, the pillar and it* arms resembling the 

 letter Y, and the interior sides of the arms being tangent* to the tube 

 of the telescope. One of these pillars is made capable of a small 

 movement in a vertical direction by turning a screw, c, at it* base, for 

 the purpose of elevating or depressing one end of the telescope and 

 spirit-tube ; and in the more perfectly constructed instruments, both 

 the pillars may be so moved. The pillars are at the extremities of a 

 strong bras* plate, r, the under side of which is connected with the 

 tripod-stand, which supports the whole instrument ; and a compass- 

 box, o, U attached immediately to the plate, as in the figure, or is 

 raised above the telescope by means of four small pillars. A hollow 

 conical socket, n, of bra** is screwed to the under side of the plate, and 

 is intended to receive a piece of bell-metal of a corresponding form, 

 which constitutes the upper part of the stand. This piece serves as a 

 vertical axis, upon which the telescope, the spirit-level, and the com- 

 pass are to turn round horizontally : sometimes, however, the conical 

 pivot projects from the under part of the plate, K K, and the socket is 

 on the stand. 



The three legs which are to support the instrument are firmly fixed 

 to a circular plate, K, perforated at its centre, and having about the 

 perforation a hollow spherical zone, resembling a small inverted cup. 

 In the simpler kinds of spirit-levels a circular plate, t, of the same 

 dimensions as the last, carries above it the pivot before mentioned ; 

 and from below it projects a stem, terminating in a ball, which fits the 

 inverted cup or socket. By means of four screws which pass through 

 one of these two plates (the upper plate in the cut), nearly at the 

 extremities of two diameters at right angles to one another, the upper 

 plate is made parallel to the horizon, and consequently the conical 

 pivot which it carries is brought to a vertical position. 



The above is a general description, which will serve nearly for 

 every spirit-level at present in use, whatever be its form ; and the 

 following is the usual manner of performing the adjustments, prepa- 

 ratory to the instrument being employed on the ground : 



The telescope should, by a proper opening of the legs of the stand, 

 be at first rendered as nearly level as can be estimated by the eye ; then, 

 being turned so as to lie vertically above the line joining two opposite 

 screws in what are called the parallel plates (K and L), the spirit-tube 

 is brought to horizontal position by relaxing the screw nearest to its 

 higher end, and tightening that wlu'ch is opposite to it : the like 

 operation is to be performed with the other pair of screws, after placing 

 the telescope vertically above them. In order to render the spirit- 

 tube parallel to the axis of the telescope, after the bubble of air has 

 been made to occupy the middle place by the process just mentioned, 

 let the telescope be reversed in the arms (the Ys as they are 

 called) ; then if the bubble does not still occupy the middle, it 

 must be made to do so by successive trials, endeavouring to correct 

 half the error by means of the screw b, and the other half by the 

 screw c. 



The eye-piece of the telescope must be moved inwards or outwards 

 till the wires in the field of view are distinctly seen ; and the object- 

 glass must also be moved by means of the pinion, M, till the station- 

 staff, placed at any convenient distance (suppose 100 yards), is also dis- 

 tinctly seen. By a few trials, the distance between the eye and the 

 object-glass may be made such that the intersection of the wires will 

 appear to remain constantly at one point on the staff while the observer 

 in looking through the telescope varies the position of his eye. It is 

 necessary besides that the intersection of the wires should be precisely 

 in the line of collimation, or the optical axis of the telescope : for this 

 purpose the point of intersection should be directed to some well- 

 defined mark at a considerable distance. The telescope must then be 

 turned on its axis ; and if the intersection remains constantly on the 

 mark, that adjustment is complete; otherwise it must be rendered so 

 by means of the screws, erf, &c., on the telescope; those screws being 

 placed at the extremities of two diameters at right angles to one 

 another, on being turned they move the plate carrying the wires in 

 the directions of those diameters. In order that the correction may be 

 mode, the apparent displacement of one of the wires, in consequence 

 of the telescope being turned half round on its axis, should be observed, 

 and the screws turned till half the displacement is corrected ; the like 

 observation and correction may then be made for the other wire : a few 

 repetitious of each adjustment will probably be necessary before the 

 error is wholly removed. 



The level constructed by the late Mr. Troughton differs from that 

 which has been above described in having the spirit-tube sunk partly 

 in the telescope ; and the latter, being incapable of a movement about 

 its axis, doe* not admit of a separate adjustment for the intersection 

 of the wires. 



Mr. Oravat, who mode considerable improvements in the mechanism 

 of these instruments, recommends the following method by which the 

 error in the positions of the cross-wires and spirit-tube may be oscer- 



