72 



APPLIANCES FOB 



Generally the pole L (Fig. 32), has a constant length 

 lift. Gin. to 16ft. 5in., and, according to the resistance R 

 of the soil or the 

 depth of plough- 

 ing, the speed, 

 v of the plough 

 is modified, the 

 speed Y of the 

 motive power 

 remainin unal- 

 tered. 

 obtained 

 creasing 



This 



IS 



by in- 



or di- 

 minishing the 

 radius r of the 

 drum. This is 

 often done by 

 inserting wooden 

 sectors, varying 

 in width, which 

 have also the ad- 

 vantage of di- 

 minishing the 

 wear of the cable 

 (Beauquesne). 

 Extensible 

 mechanisms are 

 also in use (Ver- 

 nette, 1894); the 

 radius of the 

 drum may by 

 this means be 

 varied from 12 

 inches to 20 

 inches. Finally, 

 we may use a toothed gearing. 



In Vernette's gins (Figs. 33 and 34) the drum is made of two 

 horizontal wheels, on the spokes of which cross-pieces may 

 slide, making a skeleton drum of variable diameter limited by 

 eight generatrices, kept in place by iron straps bolted at the 

 top. The diameter of this drum may vary from between 20 

 inches to 5 feet. One revolution of the capstan corresponds, 

 therefore, to a movement of the plough of from 5 feet to 

 16ft. 6in. 



