OF ARTS AND SCIENCES. 291 



neutral axis is very near the centre of the beam, as shown by the 

 fracture. 



That beams which are subjected to severe strains for a long time 

 bend more before breaking than those whicli are broke u in a compar 

 atively short time. 



That the Modulus of Elasticity of small spruce beams, of a quality 

 such as is used in the best buildinga, may be taken at from 1,600,000 

 to 1,700,000 lbs., and the Modulus of Rupture at about 11,000 lbs. 



The only other experiments on American spruce with which the 

 writer is familiar are those made by Mr. R. G. Hatfield, on small 

 beams, 1.6 feet between supports, and some experiments by Mr. 

 Thomas Laslett, of England, on pieces of Canada spruce 2 inches 

 square and 72 inches between supports. 



Mr. Hatfield gives as the average value of the transverse strength 

 of a unit beam, 612 lbs.,* which would give 11,016 lbs, for the Mod- 

 ulus of Rupture. 



From data given by Laslett f we obtain as the value of i?, 9,045 lbs. 



The value generally giveij for the Modulus of Elasticity of spruce is 

 1,600,000 lbs. 



* Hatfield's Transverse Strains, Table XLII. 



t Timber and Timber Trees, Native and Foreign, by Thomas Laslett, In- 

 spector to the Admiralty, London, 1875. 



