NATURAL PHILOSOPHY. 135 



its side, an upright pin was fixed close to the further edge of the 

 board, at the middle, to serve as the fulcrum for the indicating lever. 

 Then, four glass rods, 7 inches long and ^ in diameter, were placed as 

 rollers on different parts of this table-board, and the upper board 

 placed on them ; the rods permitted any required amount of pressure 

 on the boards, with a free motion of the upper on the lower to the 

 right and left. At the part corresponding to the pin in the lower 

 board, a piece was cut out of the upper beard, and a pin attached 

 there, which, being bent downward, entered the hole in the end of the 

 short arm of the index lever ; this part of the lever was of cardboard ; 

 the indicating prolongation was a straight hay-stalk 15 inches long. In 

 order to restrain the motion of the upper board on the lower, two vul- 

 canized rubber rings were passed round both, at the parts not resting on 

 the table ; these, while they tied the boards together, acted also as 

 springs, and while they allowed the first feeblest tendency to mo- 

 tion to be seen by the index, exerted, before the upper board had 

 moved a quarter of an inch, sufficient power in pulling the upper 

 board back from either side, to resist a strong lateral action of the 

 hand. All being thus arranged, except that the lever was away 

 the two boards were tied together with string, running parallel to the 

 vulcanized rubber springs, so as to be immovable in relation to each 

 other. They were then placed on the table, and a table-turner sat 

 down to them ; the table very shortly moved in due order, showing 

 that the apparatus offered no impediment to the action. A like ap- 

 paratus with metal rollers produced the same result under the hands 

 of another person. The index was now put into its place, and the 

 string loosened, so that the springs should come into play. It was 

 soon seen, with the party that could will the motion in either direc- 

 tion, (from whom the index was purposely hidden) that the hands 

 were gradually creeping up in the direction before agreed upon, 

 though the party certainly thought they were pressing downward only. 

 When shown that it was so, they were truly surprised ; but when they 

 lifted up their hands and immediately saw the index return to its nor- 

 mal position, they were convinced. When they looked at the index 

 and could see for themselves whether they were pressing truly down- 

 ward, or obliquely so as to produce a resultant in a right or left handed 

 direction, then such an effect never took place. Several tried for a 

 long while together, and with the best will in the world ; but no mo- 

 tion, right or left, of the table, or hand, or anything else, occurred. 

 The result was, that when the parties saw the index, it remained very 

 steady ; when it was hidden from them, or they looked away from it, 

 it wavered about, though they believed that they always pressed 

 directly downward ; and, when the table did not move, there was still 

 a resultant of hand force in the direction in which it was wished the 

 table should move, which, however, was exercised quite unwittingly 

 by the party operating. This resultant it is which, in the course of 

 the waiting time, while the fingers and hands become stiff, numb, and 

 insensible by continued pressure, grows to an amount sufficient to 

 move the table or the substances pressed upon. But the most valuable 



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