Page:The achievements of Luther Trant - Balmer and MacHarg - 1910.djvu/310

278 necessary for me to do so. For under the operation of a well-known psychological principle called Weber's Law, I knew that the same ratio of discrimination between weights holds pretty nearly constant for each individual, whether the experiment is made with grains, or ounces, or pounds. In other words, if a person's 'threshold of difference'—as his power of weight discrimination is called—is only one-tenth in grains, it is the same in drams or ounces; and if he can not accurately determine whether one stein weighs one-fifteenth more than another, neither can he pick out the heavier shell if the difference is only one-fifteenth. So I merely had to take five of your steins, fill the one I used as a standard with shot till it weighed about six ounces, or 100 drams. The other steins I weighted to 105, 107, 108, 110 drams respectively; and by mixing them up and timing both Tyler's and Chapin's answers so as to be sure they were answering their honest, first impressions of the weights of the steins and were not trying to trick me, I found that neither could consistently tell whether the steins that weighed one-twentieth, one-fifteenth or even the steins which weighed one-twelfth more were heavier, lighter or the same as the standard stein; and it was only when they got the one which weighed 110 drams and was one-tenth heavier that they were always right. So I knew."

"I see! I see!" Sheppard cried eagerly. "Then the coins you took to Findlay were—"

"Weights to try him in precisely the same sense," Trant continued. "Only they approximated much more closely the weights of the bullets and had,