The first apparatus used for the research was made as follows:  Two uprights were fastened to a table.  These supported a cross-bar about ten inches from the table.  To this bar was fastened a row of steel springs which could be pressed down in the manner of piano keys.  To each of these springs was fastened a thread which held a bullet.  The bullets, which were wrapped in silk to obviate temperature sensations, were thus suspended just above the fingers, two over each finger.  Each thread passed through a small ring which was held just a little above the fingers.  These rings could be moved in any direction to accommodate the bullet to the position of the finger.  Any number of the bullets could be let down at once.  The main object at first was to learn something about the fusion of sensations when more than two contacts were given.

Special attention was given to the relation of the errors made when the fingers were near together to those made when the fingers were spread.  For this purpose a series of experiments was made with the fingers close together, and then the series was repeated with the fingers spread as far as possible without the subject’s feeling any strain.  Each subject was experimented on one hour a week for about three months.  The same kind of stimulation was given when the fingers were near together as was given when they were spread.  The figures given below represent the average percentage of errors for four subjects.

Of the total number of answers given by all subjects when the fingers were close together, 70 per cent. were wrong.  An answer was called wrong whenever the subject failed to judge the number correctly.  In making out the figures I did not take into account the nature of the errors.  Whether involving too many or too few the answer was called wrong.  Counting up the number of wrong answers when the fingers were spread, I found that 28 per cent. of the total number of answers were wrong.  This means simply that when the fingers were near together there were more than twice as many errors as there were when they were spread, in spite of the fact that each finger was stimulated in the same way in each case.

A similar experiment was tried using the two middle fingers only.  In this case not more than four contacts could be made at once, and hence we should expect a smaller number of errors, but we should expect still to find more of them when the fingers are near together than when they are spread.  I found that 49 per cent. of the answers were wrong when the fingers were near together and 20 per cent. were wrong when they were spread.  It happens that this ratio is approximately the same as the former one, but I do not regard this fact as very significant.  I state only that it is easier to judge in one case than in the other; how much easier may depend on various factors.

To carry the point still further I took only two bullets, one over the second phalanx of each middle finger.  When the fingers were spread the two were never felt as one.  When the fingers were together they were often felt as one.