42 Experiments on the Adhesion of Iron Spikes, 
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. Jn 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 faces 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 chestaut timber, (table II. Ex. 
6,) required 1852 lbs. to extract it, the grooved and swelled spike, 
(Ex. 1, same table,) took but 1710 lbs. And in table IH. Ex. 11, 
we find the swelled spike drawn from white oak by 3727 Ibs. 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 : 
. Narrow flat spike, with a ratio of . ‘ 7.049 
Wide “6 ‘c ‘ce 73 cc , A 5.712 
Grooved but not swelled, “ “  . : 5.662 
Grooved and notched, i cach ak ‘ 5.300 
Grooved and swelled, aia. ‘ 4.624 
Burden’s patent, =“ cgi 3 4.509 
Square hammered, ‘ pinion é 4.129 
Plain cylindrical, “ aie = 3.200 
Se ere SS 
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 
