when driven into different species of Timber. 43 



drawing these spikes, the holes were almost perfectly square. This 

 resulted from the position of the rings of annual growth and the 

 greater elasticity in some directions than in others. It is probable 

 that if the filed grooves in experiments 16 and 17 had been covered 

 with a scale of oxide, as was the case with the plain spike used in 

 experiment 18, the former would have given a result somewhat 

 higher. 



When holes are drilled into stone blocks and afterwards plugged 

 with timber to receive spikes in fastening on the chairs of edge rails, 

 the method of experimenting just described finds an application, and 

 it is probable that in such cases the grooved cylinder with a conical 

 grooved point, may prove advantageous. 



A kw experiments were made to determine the effect of driving 

 to different depths, on the total amount of retention. For this pur- 

 pose two different spikes were selected, viz. the square hand-wrought 

 spike, the section of which was . 405 X. 402, and the wide flat one 

 of which the section was .539 X .288. They were respectively 

 driven to a certain depth into unseasoned chestnut, and then subject- 

 ed to a force just sufficient to start them. This force was noted, 

 and the spike was immediately driven down one inch deeper than 

 before, and the force again applied. All ray experiments proved 

 that when a spike is once started, the force required for its final ex- 

 traction is much less than that which produced the first movement. 

 This is readily accounted for on the principle that as the wedge- 

 shaped point was from half an inch to an inch in length ; and as 

 this, on the starting back of the spike a very little distance, became 

 mostly relieved from the pressure of the fibres, all that part of the 

 retention which had been due to the wedge-shaped portion of the 

 spike was at once destroyed. The following table will show, how- 

 ever, that the mere starting of the spike with parallel faces does not 

 essentially diminish the retention, when again driven into the timber 

 to a greater depth than before. But when a bar of iron is spiked 

 upon wood, if the spike be driven down until the bar compresses the 

 wood to a great degree, the recoil of the latter may become so great 

 as to start back the spike a short distance after the last blow hasbeerj 

 given. In this case a great diminution in the useful effect will be 

 the consequence. This shows that a limit may exist to the force 

 which we should apply in urging down spikes or bolts destined to 

 fasten materials together. 



