130 PRACTICAL INSTRUCTIONS REGARDING THE USE OF 



is fixed round the box of the wheel to be raised, and a man 

 acting on the other end of the lever k may easily lift very 

 heavy weights ; this instrument is more practicable than an 

 ordinary screw-jack, which could not be used in very damp 

 soils. 



The most delicate and costly part of a subsoiling plant is 

 the cable. Its strength and quality must be tested before 

 purchasing it. The only cables used now are those made of 

 steel wire, the diameter of which varies from -J inch to 0-86 

 inch. Above O86 inch they become too rigid, and do not 

 wind easily around the drums. They are generally made 01 

 four strands, each of which is again divided into four strands 

 twisted around a hemp cord. Each cable must be, when 

 purchased, wound on very strong portable drums, for, if these 

 drums break, it is very difficult and sometimes impossible to 

 unwind the cable, which has, consequently, to be cut in many 

 places, rendering it afterwards weaker. These cables must be 

 very regular in diameter, supple, yet not extensible, for when 

 they lengthen their diameter diminishes. They should resist 

 an effort of 25,800 Ibs. per square inch of section. When 

 working normally their breaking strain should be 51, 600 Ibs. 

 per square inch. In clay or clay-siliceous soils they are sup- 

 posed to work 150 days of 10 hours with a steam-winding 

 drum and a plough working at the rate of 15^ inches per 

 second ; and 450 days with a horse- winding drum and a 

 plough working at the rate of 4 inches per second. The 

 cables are guaranteed to work the above number of days, 

 on the condition, however, that they are not made to support 

 a strain greater than 25,800 Ibs. per square inch of section, 

 for above this effort of traction, which is the limit of elas- 

 ticity of the cable, it will lengthen and dislocate. Notwith- 

 standing every precaution, the cable may become entangled 

 between the flanges of the drum and get broken. The two 

 broken ends then have to be carefully spliced. This splicing 

 requires great care and special tools, which should always 

 be kept on the place two well-tempered steel cold-chisels, 

 a marline spike, made of a steel rod 0-6 to 0*8 inch in 

 diameter, well sharpened at one end, and a strong hammer. 



The two broken ends of the cable are cut with the cold-chisel 

 (Fig. 83), the strands are unlayed for a length of 3ft. lOin., 

 and fitted into each other. The ends are laced over and 

 under the strands of the opposite rope, as shown in Fig. 83, 



