Mr. C. Fox on the Construction of Skew Arches. 303 
more than the stone. In an arch where stone- and brick~ 
work are combined, little reliance should be placed on their 
connexion, as this is always more or less disturbed after the 
centring is removed, so that we should endeavour to con+ 
struct each portion of the arch with its bearing surfaces or 
beds as nearly equal as possible. 
In the first models the soffits of all the stones were made of 
an equal length, considering that this would present the best 
appearance; but this method rendered the bearing surfaces 
very unequal, as will be seen by fig. 9; the equal lengths 
being indicated by the dotted lines. 
This difficulty is overcome by this simple means: instead of 
having the stones of equal length on the soffit, they are made 
so on the intermediate development, and then the areas of 
the bearing surfaces or beds of the stones are all equal. See 
fig. 10. 
“Having given the mode of laying out the lines, I will now 
proceed to the practical part, viz. the working of the indivi- 
dual stones. 
My first idea was to commence by working the soffit; and 
this was the mode employed. 
Having obtained an elastic mould cut to the angle at which 
the joints of the soffit cross the axis of the bridge, the work~ 
man by means of this gets an oblique line on that surface of 
the stone which he intends for the soffit. It will be under- 
stood from fig. 11, that this oblique line thus obtained will be 
parallel with the axis of the bridge. The workman then pro- 
ceeds to chisel out a groove (or what is by masons called a 
chisel-draught) along this line, of sufficient depth for what he 
knows will be required for the hollowing of the stone. 
He then takes two wooden moulds (one of which is shown 
in fig. 12), which are portions of the same circle as the soffit 
itself. A mark being placed upon the centre of each of these 
moulds, the workman then proceeds to sink them into the 
stones at right angles to this chisel-draught, (see fig. 11,) and 
in such a manner that the centre marks shall be in the chisel- 
draught, and the upper edges of the moulds, which are straight, 
shall be in the same plane, or what is commonly called, out 
of winding. It will now be obvious that these two last grooves 
will form true portions of the soffit itself, and therefore, that 
the workman has nothing to do but to work out the remainder 
of the stone with a straight edge, always kept parallel with 
the first draught, and sunk to the bottom of the two draughts 
which were worked by the curved moulds. Having ob- 
tained this hollowed surface, an elastic mould, of the exact 
size of the soffit of each stone, is pressed into it, by which 
