to the operatee until his power of discrimination is approximately made out, and then to proceed more carefully.  It is best now, for reasons stated in the Appendix, to hand to the operatee sequences of three weights at a time, after shuffling them.  These he has to arrange in their proper order, with his eyes shut, and by the sense of their weight alone.  The operator finally records the scale interval that the operatee can just appreciate, as being the true measure of the coarseness (or the inverse measure of the delicacy) of the sensitivity of the operatee.

It is somewhat tedious to test many persons in succession, but any one can test his own powers at odd and end times with ease and nicety, if he happens to have ready access to suitable apparatus.

The use of tests, which, objectively speaking, run in a geometric series, and subjectively in an arithmetic one, may be applied to touch, by the use of wire-work of various degrees of fineness; to taste, by stock bottles of solutions of salt, etc., of various strengths; to smell, by bottles of attar of rose, etc., in various degrees of dilution.

The tests show the sensitivity at the time they are made, and give an approximate measure of the discrimination with which the operatee habitually employs his senses.  It does not measure his capacity for discrimination, because the discriminative faculty admits of much education, and the test results always show increased delicacy after a little practice.  However, the requirements of everyday life educate all our faculties in some degree, and I have not found the performances with test weights to improve much after a little familiarity with their use.  The weights have, as it were, to be played with at first, then they must be tried carefully on three or four separate occasions.

I did not at first find it at all an easy matter to make test weights so alike as to differ in no other appreciable respect than in their specific gravity, and if they differ and become known apart, the knowledge so acquired will vitiate future judgments in various indirect ways.  Similarity in outward shape and touch was ensured by the use of mechanically-made cartridge cases; dissimilarity through any external stain was rendered of no hindrance to the experiment by making the operatee handle them in a bag or with his eyes shut.  Two bodies may, however, be alike in weight and outward appearance and yet behave differently when otherwise mechanically tested, and, consequently, when they are handled.  For example, take two eggs, one raw and the other hard boiled, and spin them on the table; press the finger for a moment upon either of them whilst it is still spinning:  if it be the hard-boiled egg it will stop as dead as a stone:  if it be the raw egg, after a little apparent hesitation, it will begin again to rotate.  The motion of its shell had alone been stopped; the internal part was still rotating and this compelled the shell to