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form of M + (±D). If M = 0, or if it is subtracted from every measure, the residues which are the different values of (± D) will form a Scheme by themselves. Schemes may therefore be made of Deviations as well as of Measures, and one of the former is seen in the upper part of Fig. 6, page 40. It is merely the upper portion of the corresponding Scheme of Measures, in which the axis of the curve plays the part of the base.

A strong family likeness runs between the 18 different Schemes of Deviations that may be respectively derived from the data in the 18 lines of Table 2. If the slope of the curve in one Scheme is steeper than that of another, we need only to fore-shorten the steeper Scheme, by inclining it away from the line of sight, in order to reduce its apparent steepness and to make it look almost identical with the other. Or, better still, we may select appropriate vertical scales that will enable all the Schemes to be drawn afresh with a uniform slope,

and be made strictly comparable.

Suppose that we have only two Schemes, A. and B., that we wish to compare. Let L.1, L.2 be the lengths of the perpendiculars at two specified grades in Scheme A., and K.1 K.2 the lengths of those at the same grades in Scheme B. ; then if every one of the data from which

Scheme B. was drawn be multiplied by K i K22, a

series of transmuted data will be obtained for drawing a new Scheme B'., on such a vertical scale that its general slope between the selected grades shall be the same as in Scheme A. For practical convenience the