In Experimenti7ig on Timber. 247 



1st, the vertical component of the reaction at the abutments 

 multiplied by the distance at which the force acts — viz., 

 w I _ wl 



2nd, the horizontal component of the reaction acting on the 

 beam as if it were a long column, multiplied by the distance 

 at which it acts — viz., 



-^ tan. e X ~ tan. = '^ tan. '0 



2 2 4 



and adding this to the former we get 



— - X —7- tan. ^e = -— (1 + tan. ^6) = — - sec. ^ (9. 

 4 4 4 ^4 



6. Size of piece tested. — It is the practice to assume that 

 the strength of timber as a tie^ beam, or column varies 

 according to the sectional area exposed to the strain, in 

 which case the size of the specimens tested to ascertain the 

 strength of any timber, would not affect the result. This, 

 however, does not appear to be the case, for from a com- 

 parison of experiments upon large and small scantlings, the 

 results tend to prove, at all events in the case of beams, that 

 the smaller the dimensions of the piece tested the higher 

 proportionately is the moment of resistance. 



If any variation were to be looked for, the contrary 

 result might have been expected, for in cutting the wood, 

 fibres which might not run exactly along the line of the 

 piece would be cut through and their support lost, and in 

 small pieces the ratio of the surface to the interior being so 

 much greater than in large pieces the weakening result 

 would be proportionately felt. It might be said, on the other 

 hand, that in small pieces defects would not be so likely to 

 occur, but I do not attach much weight to this explanation, 

 as were this the cause of the anomaly all large pieces tested 

 would require to be subject to these defects in a uniform 

 way and reduced thereby to a corresponding state of weak- 

 ness, a state of matters highly improbable. Without 

 attempting to explain the reason, I shall simply place on 

 record the facts which seem to establish the proposition. 



Tensile strength. — Sufficient data is not obtainable to 

 warrant any conclusions being arrived at with regard to 

 tensile strength, although Laslett, who tested pieces many 

 times larger than any other experimenter, invariably obtained 

 results very much lower. 



Transverse strength. — The following table shows results 

 which appear to establish the proposition in question in 



