The instrument consists simply of a piece of wood shaped like a set-square, as shown in Fig. 1, or a diagram of the same form drawn on paper, and divided out along the two edges, which are at right angles to each other, the divisions being taken to represent inches, feet, or yards, etc., according to the kind of work for which the instrument is used. Suppose that two pipes, A and B, Fig. 2, respectively 5 in. and 4-1/2 in. in diameter, deliver into a third pipe, D, and it be required to find the proper diameter for the latter pipe. Then from 5 on the scale of one of the divided edges to 4- 1/4 on the other, draw a line, as shown dotted in Fig. 1, and the length of this line, measured with the same scale as that to which the edges are divided, will be the diameter of pipe required; in this case, 6-3/4 in. On the other hand, if a pipe, D, 6-3/4- in. in diameter, he delivered into a pipe, A, 5 in in diameter, and it was required to know what other sizeof pipe, B, could also be supplied, all that would be necessary would be to take the division point 5 on one edge as a centre, and, with 6-3/4 in. as a radius, describe an arc cutting the other divided edge. The point at which the latter edge was cut by this arc would show the diameter of pipe required,

Apparatus For Determining The Diameter Of Pipes