After the above detailed account it will only be necessary to give an outline of the other process of graduating tubes.
Fig. 39.
The standard scale to be copied, A, which may in this case be another graduated tube, or even a paper scale, and the object to be ruled, B, are securely fixed, end to end, a little distance apart, in a groove made in a board or in the top of a table. A stiff bar of wood, C, has a point fixed at D, and a knife edge at E, D is placed in any division of A, C is held firmly at E and D, and a cut is made by the knife through the wax on B, the point D is then moved into the next division, and the operation is repeated. To regulate the length and position of the cuts, B is usually held in position by two sheets of brass projecting over the edges of the groove in which it lies; the metal sheets have notches cut into them at the intervals at which longer marks are to be made.
When the scale is completed, the equality of the divisions in various parts of it may be, to some extent, verified as follows:—Adjust a compass so that its points fall into two divisions 5, 10, or 20 mm. apart. Then apply the points of the compass to various parts of the scale. In every part the length of a given number of divisions should be exactly the same. The individual divisions should also be carefully inspected by the eye; they should be sensibly equal. If badly ruled, long and short divisions will be found on the scale. Very often a long and a short division will be adjacent, and will be the more easily observed in consequence.
To Divide a Given Line into Equal Parts.—Occasionally it is necessary to divide a line of given length into x equal parts. For instance, to divide the stem of a thermometer from the freezing-point to the boiling-point into one hundred degrees.
Fig. 40.