Mr Hodgkinson on tlie Strength of Materials. 173 



to the side AB, there were small moveable pullies affixed, as G, H, I, and 

 similar pullies near the corner C, as represented on the figure ; and in the 

 intermediate space between these, as at F, there was a rectangular hole cut 

 through the board, and where the dotted line is seen there projected the ends 

 of a number of equal equidistant straight springs of iron or steel wire, which 

 were firmly inserted at their other ends into a wooden frame a be d, 

 Fie. 11, «nd this frame was then fast nailed at its ends a and d to the back 

 of the board, so that the springs between a and d might project about an 

 inch through the hole F, and be perpendicular to the plain of the board. 



I then got a very light piece of wood in the form of an isosceles triangle 

 ELM whose altitude was about 3 feet 6 inches, (the length of the 

 board) and its base LM 10 inches. Along the side of LM there was 

 nailed a piece of tin, perforated with a row of holes, so as rather loosely to 

 fit the ends of the springs projecting through F, and this tin was slid up- 

 on them The board ABCD was then raised perpendicularly to the hori- 

 zon its edge CD being uppermost, and having the triangular piece ELM 

 sliding along its side, and attached to the board only by the springs: the 

 end AD of the board serving to render the triangle steady, and, (by 

 means of a pointed instrument passing through the latter) to hold it, if 

 necessary, in any position. . 



I then hung a small weight at the end E, and there being nothing to 

 support it, and the weight of the triangle, but the springs, the point was, 

 as might be inferred, carried some distance down, the upper springs being 

 drawn after the base of the triangle, nearly in the direction CD, and the 

 lower ones made to recede in the opposite direction ; the whole turning 

 as it were on the central spring, which was not bent, and consequently 



supported nothing. ,'■«.■ 



I next attached a weight w to a point of the triangle near to L, 64 in- 

 ches from the central spring, by a string passing over the pully I, and an 

 equal weight w' to another point, ± an inch on the other side of that 

 sprino, and increasing the weight at E, so as to bring the base LM per- 

 pendicular to the horizon, (which was done in all the experiments,) I 

 found that the whole turned round the central spring as before, though 

 the distances of the equal weight from the central spring were as 13 



t0 1 afterwards put weights to other points, passing over all the pullies, 

 6 H I, at once, putting sometimes a large one over G, and a small one 

 over I, and sometimes the reverse j and, doing in like manner by the 

 pullies near the corner C, I found that the apparatus always turned 

 round the central spring, without its being bent, when the sums of the 

 weights on each side were equal. But, if the sums of the opposing weights 

 were unequal, the triangle no longer turned round the central spring, but 

 round some other point, at which there was an equality between the ne- 

 gative and affirmative forces. , . 



It is evident that we might have substituted for the weights in the 

 above experiments springs, which would have beer, unbent, when those 

 which are in the instrument were so, and which (when bent so that the 

 triangle might assume the position it wns in during the experiments,) 



