when driven into different species of Timber. 



37 



The third and fourth experiments were made with the same spikes 

 respectively as the first and second ; but instead of yellow pine, the 

 timber employed was thoroughly seasoned white oak. 



The plain spike driven 3f inches into that timber, required for its 

 extraction a force of 3,910 lbs. and, as before, exhibited no signs of 

 movement until the instant of starting, when it suddenly came out 

 about i of an inch, or as far as the range of motion and the elasti- 

 city of the machine would permit. 



The flanched, swelled and grooved spike, driven 3f inches into 

 mother part of the same piece of plank, from which the plain one 

 nad been extracted, was drawn out with a force of 3,791 lbs. A 

 slow motion to the extent of -^^ or -^\ of an inch was, in this trial, 

 perceived to precede the starting of the spike ; and was accompa- 

 nied by a gradual protrusion of the fibres of the timber Immediately 

 around the iron. In these experiments, though the plain spike bore 

 the greater absolute weights, yet when the weight of metal is con- 

 sidered, it is seen that the relative values of the two are 4.515 in 

 the plain, and 5.354 in the grooved form. The various circum- 

 stances of the four preceding experiments are seen at a single view 

 in the following table. 



Hence it appears, that in yellow pine the grooved and swelled 

 form was about 5 per cent, less advantageous than the plain, while 



