when driven into different species of Timber. 39 



The first five of the preceding experiments show that with a spike 

 of given form, and driven a certain distance into different timbers, 

 the order of retentivenoss, beginning with the highest, is as follows : 

 1, locust; 2, white oak; 3, hemlock ; 4, unseasoned chestnut ; 5, 

 yellow pine. From the 6th, Tth and 8th experiments, we see that 

 chestnut is still above yellow pine, but that hemlock is inferior to 

 both. By the 9th and 10th, it also appears that hemlock is still to 

 be placed below chestnut. Comparing the 1st experiment in this 

 table with the 6th, and the 2nd with the Tth, we perceive that the 

 swell towards the point of the spike, was so far from being an ad- 

 vantage to it, that it in fact rendered the spike less retentive than 

 when that swelled part had been removed ; so that, even could this 

 form have been produced without any increase in the weight of the 

 spike, it would still have been less advantageous than the simple 

 groove without the swell : but when it is considered that the swell 

 added 47 grs. (—■806 -759) to the weight, it is evident that the 

 groove alone has a decided advantage over the other form. By 

 the trials in unseasoned chestnut, (Nos. 1 and 6.) this advantage is 



2440 — 2121 



15 per cent. : thus oVo] "^ 1^' ^"^^ ^Y those on yellow 



2328 — 2069 ^ ^ 



pine, (Nos. 2 and 7,) it is onfiQ = 12.5 per cent. In fact, 



after the ends of the fibres have once been thrust apart by the thick 

 part of the swell, it is evident that when they come opposite to the 

 cavity above the swell they must lose some portion of their power to 

 press the spike and produce the retaining force of friction ; this force 

 must then depend for its production on the action of those fibres of 

 the wood which are opposite to the swelled portion, or between it 

 and the point of the spikes. 



In the next series of experiments, it was attempted to ascertain 

 the relation between forms more diversified than had hitherto been 

 employed. 



As it is evident that the total retentiveness of the wood must de- 

 pend, in a considerable degree, upon the number of fibres which are 

 longitudinally compressed by the spike, it was inferred, that on the 

 area of the two faces, which in driving the spike are placed against 

 the ends of the fibres, must in a great measure depend the retention 

 of the spike. In this series, four kinds of wood and ten forms of 

 spikes were employed. 



