THE FORM AND MANUFACTURE OF SHOES. 59 



carries the nails, and the inner groove lightens the shoe 

 and increases the foot-hold. It is not the number of 

 grooves or ridges that prevents slipping; it is the absence 

 of a continuous flat surface of iron, and the existence of 

 irregularities which become filled up with sand and grit. 

 A four-grooved shoe has no more anti-slipping j^roper- 

 ties than a three-grooved, and a one-grooved shoe is as 

 good as either, although it cannot stand the same 

 amount of wear. 



Transverse ridges and notches have also been tried 

 as ground-surfaces for shoes, but offer very little, if any, 

 better grip than the longitudinal grooves. Their great 

 disadvantage is that they cannot be mads deep enough 

 without weakening the shoe, whilst, if shallow, thej'' ara 

 worn out before the shoe has been long in wear. 



Fig. 38. — Ground-surfaces, notches, project! ons„ ridges. 



A Calkin is the name given to the extremity of a 

 shoe when turned down at the heels. Calkins are used 

 on most hind shoes and, in some parts of the country, on 

 fore shoes. They are supposed to be the most convenient 

 and effective means of giving good foot-hold. This sup- 

 position is correct when a horse travels on soft ground 

 or on streets so paved that a space is left between each 

 course of stones. They are of very little use on asphalt 

 or wood pavement and not much more use on roller- 



