This condition he can scarcely be said to have fulfilled.
With polar distances of 1/2 inch and 1 inch, the machine works
unsatisfactorily, which indeed might have been foreseen from the
construction of its sliding bars. It works best from 2.5 inches to 5
inches, and this is the range to which I think we ought to confine the
present type of instrument. As the last conditions I may note that:
6. A practical integraph ought to be easy to read.
7. Draw a good clear curve.
The scale on the present instrument is very inconvenient, as it is
often almost out of sight; the curve it draws, on the other hand, I
consider very satisfactory, when the pencil is loaded, say, with a
planimeter weight. On the whole, I think you will agree with me that
this integraph goes a good way, if not the whole way, toward
fulfilling the conditions of a practical instrument.
I next turn to its construction and the claim it has to be considered
in any way new. Let me briefly remind our members of the process by
which an element Q R of the sum curve (Fig. 1) corresponding to the
point P on the primitive is drawn; P M being the mid-ordinate of L N,
a horizontal element, P B is drawn perpendicular to any vertical line
A B; and O A being a constant distance termed the base or "polar
distance," Q R is drawn between the ordinates of L and W, parallel to
O B.
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