OP ARTS AND SCIENCES. 285 



XIV. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XIV. EXPERIMENTS ON . THE STRENGTH AND 

 STIFFNESS OF SMALL SPRUCE BEAMS. 



By F. E. Kidder. 



Presented by Prof. Charles R. Cross, Feb. 9, 1881. 



The object of the following experiments was to determine the 

 Moduli of Elasticity and Rupture in small beams of white spruce 

 (Abies alba) ; and such other information as might be derived from 

 the data obtained. 



The machine used for the purpose consists of two solid wooden 

 frames, carefully levelled and placed forty inches apart. Upon the 

 top of each frame is placed a movable plate of iron, which is care- 

 fully adjusted so that the two plates shall be directly opposite each 

 other, and exactly forty inches apart between the faces. These plates 

 form the supports for the beams. 



The loads were applied by means of a scale pan suspended from a 

 three-quarter inch bolt, which rested upon the centre of the beam. 

 By means of an iron strap suspended from a horizontal beam placed 

 above the test piece, and resting on two screws, the bolt from which 

 the load was suspended could be raised from or lowered upon the test 

 piece as easily and gradually as could be desired. 



The deflections of the beams were measured by means of a microm- 

 eter screw, reading to one ten-thousandth of an inch. As the bolt 

 from which the load was suspended rested on the centre of the beam, 

 it was necessary to measure the deflections at a distance of one inch 

 from the centre ; but the deflections used in calculating the values of 

 the Modulus of Elasticity were corrected so as to give the deflection 

 at the centre, supposing the curve assumed by the beam to be the arc 

 of a circle ; from which, in fact, it deviates but little under such small 



