Fig. 95.—Section of semi-cylindrical staff.
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261.—Semi-circular Staff.—This is another kind of telescopic staff, with Sopwith sliding arrangement, which possesses a certain merit, but is more expensive to make. It is semi-cylindrical, the cylindrical part being made without any joint. This is shown in the section Fig. 95. The general dimensions of the face of the staff are the same as those given for the Sopwith staff. This staff is a little stiffer, but there is more risk of its not standing true. As in the union of four pieces of wood in the square form, previously described, the tendency of one piece to warp in a certain direction is resisted by the other pieces; but in this cylindrical form there is no such resistance, so that it is found that these staves when exposed to wet are much more liable to become warped and fixed in their slides. There is also more difficulty in getting the conical form fairly accurate in the working. One particular merit, when a pair of staves of this kind is used, is that the two go together and form a cylinder, which is a very compact form, but perhaps a little more difficult to carry, owing to the tendency of a cylinder to roll off the shoulder.
Fig. 96.—Sopwith pattern staff.
Fig. 97.—Field's pattern.
Fig. 98.—Stanley's old pattern.
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262.—What was originally considered as the defect of the Sopwith staff, besides its shakiness, as it was first made, was the diminished width of reading of the upper length, this being only 1¼ inches wide. This caused for a long period other forms of staves, which maintained the same width of reading surface quite to the top, to be preferred by many. This fault has been partly remedied by the author in making the feet readings of the upper staff by dots, instead of the narrow figures, which were very difficult to read. In other respects the light and portable form of the Sopwith staff has ensured its general use.
