mth Reference to the Experivients of Mr. P. Barlow, Jun. 1 1 7 



is gained by considering the weight of the timber, except in 

 the particular case where the question is the deflection of a 

 beam from its own weight," I must therefore be allowed to 

 show that this remark has been rather inadvertently made; 

 and I doubt not that Mr. Barlow will, upon further consi- 

 deration, see that in almost all buildings and machinery, the 

 weight of the materials used in their construction is a most 

 essential matter of consideration. There may be some few 

 constructions which would be improved by an increase of 

 weight; but generally the value of materials will be estimated 

 in the direct ratio of the strength, and inversely as the weight, 

 when the durability and other qualities remain the same: thus 

 if a new species of wood, equal in durability to oak and teak, 

 could be found of equal strength, but of half the specific gra- 

 vity, would it not be preferred for almost all purposes botli in 

 naval and civil architecture, and for machines of almost every 

 description? The same may be said of metals, — the less the 

 weight, and the greater the strength, the more valuable they 

 •will be. 



If I could construct a crane for moving heavy loads with 

 good Memel timber, at half the expense and of two-thirds 

 the weight of one made of Locust-tree, — should I be excused 

 in adopting the Locust-tree on account of saving two or three 

 cubic feet of wood ? 



I am ready to admit that there are cases in which space is of 

 importance, as well as strength, but in such cases iron and 

 steel are preferred to wood. It is not my intention to repre- 

 sent that lightness and strength are the only qualities to be 

 attended to, well knowing that other qualities for particular 

 purposes are of importance: but the present discussion does 

 not involve those considerations, but simply the strength, re- 

 lative to the weight; so that when all other things are alike, 

 the value will be in proportion to the height of the modulus 

 of elasticity. 



To render the subject a little more plain, we' may calculate 

 the quantity of timber required to form a beam of 20 feet 

 length of bearing, to support a given load, to which a deflec- 

 tion of half an inch may be allowed. This beam, if made of 

 Tonquin Bean, will require about 16^ cubic feet; and if made 

 of Memel timber of the same breadth, will require about 19f 

 cubic feet to possess the same strength ; but the Memel beam 

 will only weigh frds of the Tonquin beam, or 370 pounds less, 

 and has therefore the advantage in point of weight. In point 

 of cost, it will depend upon the price per foot of each species. 

 Should the Toii<|iiin beam be "s. 6l(l., while the Memel cost 

 3i-. per foot, the cost woidd be alike: except, therefore, this 



