<< Previous Section Table of Contents The Polar Planimeter Page Numbers Next Section >>

CHAPTER IX.

Quantities of Materials (Cont'd.)

IV. Special Methods of Measurement of Quantities.

1. Volumes of Brickwork.

Method of Measurement.

To illustrate the use of the table in this connection, let us suppose Fig. 6 of Plate V to be the cross-section of a tunnel to be lined with brick in the manner shown, the irregularities of the tunnel to be filled in with brickwork, and that we desire to know the number of brick used per linear foot, the drawing being made to a scale of ¼ inch to 1 foot.

Looking in Table 10 we find the setting for the given scale to be 285.6 and the value of the Relative Vernier Unit to be 4.0.

Adjusting the Planimeter to the given setting, and having brought the instrument to a Zero reading the area of the cross-section of the brick lining is traced in the usual manner. Let us suppose the reading of the instrument for this tracing to be say 9256 Vernier Units. Then since the value of the Vernier Unit for this scale is 4.0 we have

9256 × 4 = 37024
which is the number of brick per linear foot required.

It is evident that since the Planimeter gives the number of brick per linear foot for the area traced, the quantities of brick in house walls and similar forms of construction is at once obtained in exactly the same manner by simply tracing the elevation of the wall directly on the plan of the building and multiplying the result by the required correction for any given thickness of wall other than 1 foot. The openings for door or windows can be traced but ordinarily this is not done in the measurement of house walls, the walls being usually counted as solid to allow for the extra work involved in the construction of such openings.

If, as is often the case and especially in retaining walls or foundations the result is required in Cu. Ft. or in Cu. Yds. instead of number of brick, Table 3 or Table 3¹ would be used respectively in place of Table 10 the operation however being exactly the same in each case whichever Table were employed.

In the preparation of the Table the average number of brick per Cu. Ft. was taken as 18.5 brick which will be found to be a very close approximation, and any result obtained by the use of Table 10 can be at once reduced to Cu. Ft. or Cu. Yds. by simple multiplication.

The method of finding the factors given in this Table is easily seen from the general Equations and mathematical discussions given in Chapter III and need not be repeated here. The Table is intended to cover every possible case in the measurement of brickwork and factors are given for every scale to which plans for brickwork are usually drawn.

<< Previous Section Table of Contents The Polar Planimeter Page Numbers Next Section >>