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