vjlien driven into different species of Timber, 35 



be supposed. Owing to the high price of iron, the flat rail is often 

 unavoidably adopted in preference to the edge rail ; and whenever 

 the speed of a train descending by gravity, or impelled with great 

 velocity by the moving power, is to be suddenly checked by the 

 brake, the friction of the periphery of the wheel on the rail, tends 

 to drive the latter lengthwise, and thus to force all the spikes with 

 which it is fastened into closer contact with the ends of the fibres 

 which have been cut in driving them. If this partial or total drag- 

 ging of the wheels along the rails take place, sometimes in one di- 

 rection, and sometimes in the other, the spikes must be subjected to 

 alternate impulses on opposite sides. Indeed, whenever the motive 

 power depends on friction for its efficacy, as in the case of the com- 

 mon locomotive engine, there is a constant succession of these two 

 opposite dragging forces, the engine constantly tending by its driving 

 wheels to urge the rail backwards, and the train by an equal but 

 more extensively distributed action tending to urge forward all the 

 rails over which it is at the same moment passing. So decided is 

 this influence, that on a rail road where the transportation is all in 

 one direction, and where the cars descend by gravity, I have seen 

 rails entirely detached, or remaining loosely connected but by a sin- 

 gle spike, while others clearly indicated by the inclined position of 

 their upper faces or heads, that they were pressed into an oblique or 

 leaning position in the w'ooden sill. 



This single case may serve to show the importance of attending 

 to the character of the spikes used in similar constructions. 



To determine some of the points relating to the forms of spikes, 

 and the kind of timber into which they are driven, the following ex- 

 periments were undertaken. They serve to show the relative econo- 

 my of each form of spike, as well as its fitness for the purpose in- 

 tended. The mode of executing the experiments was, to drive each 

 spike to a certain distance above its cutting edge, into the edge of a 

 piece of plank or scantling, and by means of a suitable apparatus, 

 adapted to that purpose, to draw it out by a direct longitudinal strain. 

 The machine employed for this purpose was the same as that which 

 has been used for testing the strength of iron and copper, in experi- 

 ments on the tenacity of materials employed in steam boilers. A 

 strong band or strap of iron, connected with the weighing beam of 

 that machine, held the piece of plank, and a clamped pincers, with 

 a suitable jaw, for taking hold of the head and projecting part of the 

 spike, was attached to the opposite part of the machine, which being 



