SPECIAL SUBSOILEKS. 101 



" We have used, and also seen, Guibal's subsoiler, in use ; 

 compared against others, such as Smith's or Reed's machines, 

 the work of the former has always been more satisfactory. 



" For travelling this machine on roads ordinary wheels are 

 fixed to the axle a preventing the teeth from touching the 

 ground. We cannot end this chapter without stating that, 

 in our opinion, it is one of the best machines, and destined to 

 render great service in intense culture." ' 



Guibal's machine was very unstable ; it had a tendency to 

 tilt sideways, and had to be kept vertical by a man acting 

 on a lever prolonging the axle. Holland, professor at 

 Grand-Jouan, thought of fixing two wheels to the frame, 

 and had a machine made to his own designs for Baron 

 Thenard, who called the machine " digger" and improved it 

 in several details, notably in mounting the wheels on a bent 

 axle, which could be raised by means of a lever. A descrip- 

 tion of it is given in the Journal <$ Agriculture Pratique, 

 1858, vol. 1, p. 220. 



Thenard's digger (Figs. 65 and 66) consists of two large 

 parallel wheels 6ft. 6in. in diameter, 4 inches apart, and 

 running loose on the axle ; the spokes are made of wood, 

 and the iron tires provided with curved tines 11 inches 

 iu length. Each wheel weighs 660 Ibs. The frame is 

 provided with a paddle-board as in Guibal's machine. 



Fig. 65. - Thenard's Digger at work. 



The axle, 2 inches in diameter, has two. bends at 

 right angles 11^ inches in length, and is terminated by 

 two axle arms, upon which ordinary wheels revolve, for 

 moving the machine about. The whole appliance is fixed 



* Guibal applied the same principle to the construction of hoeing rollers, 

 used for surface work (length, 3ft. llin.; diameter, 21 inches ; length of 

 teeth, o inches). 



