TRANSACTIONS OF THE SECTIONS. 155 



Mr. Sopwith described the improvements made by him in the con- 

 struction of these staves, and also the use of a stave for subterranean 

 leveling, the face of which is protected by a glass shield. It is hinged 

 so as to admit of being used in any seam of coal from 3 to 5 feet in 

 height ; and the same principle may be applied to any greater or less 

 extent. Mr. Sopwith stated, that from the experience of himself and 

 assistants in conducting extensive leveling operations, fully one half 

 time is gained, as well as great additional accuracy. 



Description of Instruments to facilitate the Drawing of Objects in Iso- 

 metrical Projection. By Thomas Sopwith, F.G.S. 



Mr. Sopwith exhibited several instruments, diagrams, &c., adapted 

 to facilitate the process of isometrical projection. The first of these is 

 a set of triangular rulers, the angles of which are coincident with the 

 angles in the isometrical projection of a cube ; and hence they can be 

 applied with great ease and rapidity to the delineation of geometrical 

 forms in isometrical draAvings. 



Isometrical squares and circles engraved on drawing-paper are 

 adapted to facilitate this mode of projection. The circles are gradu- 

 ated; and hence any angles, whether on a horizontal or vertical plane, 

 can be correctly delineated and subsequently measured. Mr. Sopwith 

 illustrated the advantages of this method of drawing by several exam- 

 ples of its application to astronomy, to architecture, and to constructive 

 designs generally. One remarkable property of isometrical drawings 

 was pointed out, viz. that drawings made on a flat surface may have 

 other flat surfaces pasted on by an edge, and which will appear in true 

 projection when turned over upon the edge, and horizontal and vertical 

 movements may be thus shown in one drawing ; thus forming what may 

 be appropriately termed a picture model. 



The Isograpli is an entirely new instrument, invented by Mr. Sop- 

 with, for transferring plans from orthographical to isometrical projec- 

 tion. This is eff'ected by means of a simple mechanical movement. 

 The isograph consists of a number of parallel rulers, made of brass or 

 ivory, the fiducial edges of which are an inch distant. These rulers 

 are fixed at each end by pivots to two brass bars, the centre of each 

 pivot exactly coinciding with the line of each fiducial edge. A brass 

 gauge is used to fix this series of rulers so as to form a true geome- 

 trical square ; and when in this position, the principal lines or points 

 are marked off" upon the respective edges of the rulers. The instru- 

 ment is then moved into a lozenge shape, and a gauge, equal in length 

 to one side of the square, is fitted so as to form the shorter diagonal. 

 Hence the opposite angles of the instrument are respectively 60° and 

 120", which is the required condition of isometrical projection. 



The Isometrical Protractor, made of brass, is used for the delinea- 

 tion of bearings in isometrical projection. A representation of a mi- 

 ning district and a plan of Newcastle, drawn isometrically, were exhi- 

 bited. 



