|------------------------------------------------------

----------------|
|                     |   Number of Families  |   Number of Children   |
|                     |--------+--------------+------------------------|
|                     | Factory| Agricultural | Factory | Agricultural |
| Within outline      |   541  |   436        |   903   |   778        |
| Between outlines    |   375  |   476        |  1233   |  1562        |
| Beyond outlines     |    84  |    88        |   545   |   571        |
|=============================================+=============

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| Total               |  1000  |  1000        |  2681   |  2911        |
|===========================================================

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C —­ AN APPARATUS FOR TESTING THE DELICACY WITH WHICH WEIGHTS CAN BE DISCRIMINATED BY HANDLING THEM.

  [Read at the Anthropological Institute, Nov., 1882.]

I submit a simple apparatus that I have designed to measure the delicacy of the sensitivity of different persons, as shown by their skill in discriminating weights, identical in size, form, and colour, but different in specific gravity.  Its interest lies in the accordance of the successive test values with the successive graduations of a true scale of sensitivity, in the ease with which the tests are applied, and the fact that the same principle can be made use of in testing the delicacy of smell and taste.

I use test-weights that mount in a series of “just perceptible differences” to an imaginary person of extreme delicacy of perception, their values being calculated according to Weber’s law.  The lowest weight is heavy enough to give a decided sense of weight to the hand when handling it, and the heaviest weight can be handled without any sense of fatigue.  They therefore conform with close approximation to a geometric series; thus—­
    WR0, WR1, WR2, WR3, etc.,
and they bear as register-marks the values of the successive indices, 0, 1, 2, 3, etc.  It follows that if a person can just distinguish between any particular pair of weights, he can also just distinguish between any other pair of weights whose register-marks differ by the same amount.  Example:  suppose A can just distinguish between the weights bearing the register-marks 2 and 4, then it follows from the construction of the apparatus that he can just distinguish between those bearing the register-marks 1 and 3, or 3 and 5, or 4 and 6, etc.; the difference being 2 in each case.

There can be but one interpretation of the phrase that the dulness of muscular sense in any person, B, is twice as great as in that of another person, A. It is that B is only capable of perceiving one grade of difference where A can perceive two.  We may, of course, state the same fact inversely, and say that the delicacy of muscular sense is in that case twice as great in A as in B. Similarly in all other cases of the kind.  Conversely, if having