upright strip with a slot, through which was passed another strip which extended back over the hand.  This latter strip could be raised or lowered by means of adjusting screws in the upright strip.  On the horizontal strip were pieces of wood made so as to slide back and forth.  Through holes in these pieces plungers were passed.  At the bottom of each plunger was a small square piece of wood held and adjusted by screws.  From this piece was suspended a small thimble filled with shot and paraffine.  The thimbles were all equally weighted.  Through a hole in the plunger ran a thread holding a piece of lead of exactly the weight of the thimble.  By touching a pin at the top this weight could be dropped into the thimble, thus doubling its weight.  A screw at the top of the piece through which the plunger passed regulated the stop of the plunger.  This apparatus had three important advantages.  It was entirely out of sight, it admitted of rapid and accurate adjustment, and it allowed the weights to be doubled quickly and without conspicuous effort.

For the purpose of studying the influence of weight on the judgments of number I began a series of experiments to train the subjects to judge one, two, three, or four contacts at once.  For this the bare metal thimbles were used, because it was found that when they were covered with chamois skin the touch was so soft that the subjects could not perceive more than one or two with any degree of accuracy, and I thought it would take entirely too long to train them to perceive four.  The metal thimbles, of course, gave some temperature sensation, but the subject needed the help and it seemed best to use the more distinct metal contacts.

In this work I had seven subjects, all of whom had had some experience in a laboratory, most of them several years.  Each one took part one hour a week.  The work was intended merely for training, but a few records were taken each day to see how the subjects progressed.  The object was to train them to perceive one, two, three, and four correctly, and not only to distinguish four from three but to distinguish four from more than four.  Hence five, six, seven, and eight at a time were often given.  When the subject had learned to do this fairly well the plan was to give him one, two, three, and four in order, then to double the weight of the four and give them again to see if he would interpret the additional weight as increase in number.  This was done and the results were entirely negative.  The subjects either noticed no difference at all or else merely noticed that the second four were a little more distinct than the first.

The next step was to give a number of light contacts to be compared with the same number of heavy ones—­the subject, not trying to tell the exact number but only which group contained the greater number.  A difference was sometimes noticed, and the subject, thinking that the only variations possible were variations of number and position, often interpreted the difference as difference in number; but the light weights were as often called more as were the heavy ones.