42 Experiments on the Adhesion of Iron SpiJ^es, 



a breadth of only .390, required as much force to extract it, as one 

 of which the breadth was .405, though the thickness of the former 

 was but .253, while that of the latter was .402 ; and on chestnut, 

 the thinner, narrower, and lighter spike, required absolutely more 

 force to withdraw it than the other. This leads us to notice the 

 different kinds of action of the respective spikes on timber of vari- 

 ous kinds. In the softer and more spongy kinds of wood, the fibres 

 instead of being forced back longitudinally and condensed upon 

 themselves, are, by driving a thick, and especially a rather obtusely 

 pointed spike, folded in masses backward and downward so as to 

 leave in certain parts the/aces of the grains of the timber in contact 

 with the surface of the metal. 



That the view just presented is correct, seems also probable from 

 what was observed in the case of the swelled spike. For while the 

 grooved but unswelled one, driven into chestnut timber, (table JI. Ex. 

 6,) required 1852 lbs. to extract it, the grooved and swelled spike, 

 (Ex. 1, same table,) took but 1710 lbs. And in table III. Ex. 11, 

 we find the swelled spike drawn from white oak by 3727 lbs. and the 

 grooved but not swelled one, Ex. 12, requiring 4247. Hence it ap- 

 pears to be necessary, in order to obtain the greatest effect, that the 

 fibres of the wood should press the face as nearly as possible in 

 their longitudinal direction and with equal intensities throughout the 

 whole length of the spike. Arranging the spikes according to the 

 order of their ratios of retention to weight, as given by the experi- 

 ments in table III, from five to twelve inclusive, we have the fol- 

 lowing : 



1. Narrow flat spiJce, mth a. ratio o[ . . . 7.049 



2. Wide " " " " " . 



3. Grooved but not swelled, 



4. Grooved and notched, 



5. Grooved and swelled, 



6. Burden^s patent, " 



7. Square hammered, " 



8. Plain cylindrical, " 



5.712 

 5.662 

 5.300 

 4.624 

 4.509 

 4.129 

 3.200 



Experiments 16, 17 and 18, of the same table, were made by 

 driving the spikes which were cylindrical with conical points into the 

 timber endwise of the grain. This method of comparing two forms, 

 the one grooved and the other plain, was adopted on account of the 

 extreme liability of the timber to be split by driving spikes of these 

 forms across the direction of the fibres. It was observed that on 



