210 Transactions of the 



resist the strains to which it is so frequently subjected from the 

 concussions of her roving compeers, which horizontal courses would 

 be less competent to withstand, and the first formed portion of the 

 tube, being more densely blended with the gelatinous cement, 

 assists it, by reason of the resilience so afforded, to yield somewhat 

 to such shocks, which at this particular point produce the greatest 

 effect in tending to rupture the tube. 



It will be readily comprehended that the foregoing particulars 

 impose very delicate manipulation in the several processes involved 

 in setting out the tube, more especially as it is intended in the 

 present instance that the top of the tube shall incline somewhat 

 towards the observer, and as this condition governs the outlines of 

 every individual pellet of each and every course throughout its 

 whole length both of the parallel and tapering portions, it demands 

 our special and attentive consideration ; and as the preliminary 

 operations require to be clearly defined, I will take as a first example 

 a single pellet more highly magnified, lying on the plane imposed 

 by the inclination of the tube, and inclined at an angle of 45°. 



First draw the pellet in outline on ])lan at the required angle. 

 Fig. 1, Plate LXXXIII. Next describe circles representing the 

 diameters of the shoulder and small end. Fig. 2 ; then divide one- 

 half the circumferences into any convenient number of points, 

 taking six in this instance, of a regular form, which will be given 

 by the set-square of 30° and 60° (but varying in number and dis- 

 position in irregular forms according to circumstances), identify 

 these points on Fig. 2 by numbers from the central point to 6 

 consecutively, and from each point draw parallel lines extending 

 indefinitely in the direction in which it is desired to show the 

 finished view ; then project the points 1, 2, 3, vertically on to any 

 horizontal line for each end a, h; prick them ofi" on the edge of 

 a slip of paper and transfer them on to the ^j?a%. Fig. 1, when by 

 projecting vertical lines from each of these numbers from Fig. 1, 

 their respective intersections with the coincident lines from Fig. 2 

 will give certain points that limit the outline of the upper half of 

 Fig. 3, and the lower half being simj^ly the reverse of this, the 

 continuance of these vertical lines, at right angles with the axis, to 

 their intersections with the horizontal lines 4, 5, and 6, will com- 

 plete the figure of the shoulder of the pellet ; the small end and 

 tapering point being set out in a similar manner. 



The projection of the complete tube now claims our attention, 

 and this should be proceeded with by drawing half plans of the 

 top and bottom. Figs. 4 and 8, at convenient distances from the 

 position to be taken by the elevation, Fig. 7, first by describing 

 semicircles cutting the shoulders of the pellets, and to set out 

 accurately on each of these their radiating axes, when for the sake 

 of distinction it will be advisable to indicate the positions of the 



