242 Mr. Bevan on the Strength of different Kinds of Wood. 



being nearly two-thirds of the ultimate strain, instead of one- 

 third, which would have been less likely to have impaired the 

 texture of the specimen. 



In experiments of this nature, it would have been more 

 satisfactory if Mr. Barlow had said something about the time 

 during which the specimen was under pressure; as the deflection 

 increases with the time, especially when the load bears so great 

 a proportion to the breaking weight. 



Instead of the proportional numbers, adopted by Mr. Bar- 

 low to express the elasticity, I beg leave to suggest that it 

 would have been more generally useful if the modulus of elasti- 

 city had been given. And to enable your readers to compare 

 the relative stiffness of the several si^ecies of wood in his ex- 

 periments, I hereby send you the approximate result as de- 

 duced by a very simple application of the slide-rule. Thus 



a I 4500 Feet modulus of elasticity 



b I Specific gravity. weight in lbs. 



from which it will be found that the mean modulus of the 

 several species of wood in the table of Mr. Barlow will be 

 nearly as follows : 



Feet. Feet. 



American Birch... 5-295000 

 Common Birch.... 5*420000 



Ash 4.-150000 



Elm 3-135000 



ChristianiaDeal... 5-305000 

 MemelDeal 6-260000 



Oak 3-303000 



Tonquin Bean . . 5-795000 



Locust 4-695000 



Bullet 5-890000 



Greenheart 6-105000 



Cabacally 4-730000 



African Oak.... 5-532000 



Hence it appears that when compared with their own weight, 

 (although probably the specimens were superior to the ordi- 

 nary quality,) none of those tried by Mr. Barlow possess a 

 greater degree of stiffness than Memel deal. 



It would have added much to the value of the above expe- 

 riments if Mr. BarloAV had given the ultimate deflection. If 

 he has the means of giving this information, it will add to the 

 gratification of many of your readers; and to none more than 

 to your humble servant, 



B. Bevan. 



P. S. — If the price per foot, at which the new species of 

 wood above named can be procured, could be communicated, 

 it would be an additional favour. 



[Various papers by Mr. Bevan, detailing the results of his experiments on 

 the strength of cohesion, elasticity, and modulus of torsion of different species 

 of wood, will be found in Phil. Mag. vol. Ixviii. pp. 112, 181, and 269; and 

 in Phil. Mag. and Annals, N. S. vol. v. p. 51, sind vi. p. 410. — Edit.] 



XXXIII. An 



