OF ARTS AND SCIENCES. 289 



lbs. were considerably greater than in the other beanis under the same 

 loads. 



Piece No. 5 gave a very high breaking weight, and broke very sud- 

 denly, more like the harder kinds of wood. Ti)e fracture was very 

 perfect, the upper half of the fibres being very evidently compressed 

 and the lower half suddenly pulled apart, with almost no splintering. 

 This piece had a small knot on the upper side, five inches from the 

 centre of the beam, but it appeared to have no effect upon the strength 

 of the beam. 



Piece No. 4 broke in a rather peculiar manner. While under a 

 load of 575 lbs., the lower fibres for about a depth of one-tenth of an 

 inch snapped apart, and the beam gradually settled down until the 

 next layer of fibres had apparently the same deflection as did the 

 lower ones at the time of breaking, when they also snapped, making a 

 layer of about the same thickness. In this way the whole lower half 

 of the beam seemed to divide itself into layers of about one-tenth of 

 an inch thick, and to break separately under about the same deflec- 

 tion, so that the beam was a long time in breaking. 



Observing that under every load that had been applied the deflection 

 kept increasing with the length of time the weight remained on the 

 beam, piece No. 7 was subjected to a load of 275 lbs. for ninety -eiglit 

 hours, during which time the deflection increased 0.079 inches. The 

 weight was then taken off and the beam allowed to recover for twenty- 

 four hours, when it had a set of .0446 inches. The same weight was 

 again applied, and it was found that the deflection, obtained by taking 

 the difference between the readings of the micrometer just before and 

 after the weight was applied, was less than it was the first time the 

 weight was applied, and the rate of increase of the deflection was 

 about the same as before. The beam was thus subjected to a weight 

 of 275 lbs. for three hundred hours in all, after which it was broken in 

 the same manner as the others. It was expected that the effect of 

 such a severe strain for so long a time would diminish its strength ; 

 but, on the contrary, it appeared to increase it, as the beam gave a 

 higher Modulus of Rupture than any of the others, although it did 

 not appear to be of as good quality as many of them. The ultimate 

 deflection of this beam greatly exceeded that in any of the others. 



Table III. shows the deflection of each beam under loads of 30, 

 40, 100, 400, 500, and 550 lbs., immediately after the load was ap- 

 plied, and at a distance of one inch from the centre. The small 

 figures under each deflection show what it would be if Hooke's Law 

 held true, taking the deflection under 30 lbs. as the starting-point. 



