370 Five Years Progress of Steam Cultivation. 
rope will always hold itself clear above the land, even upon low 
rope-porters : but a slack or outgoing rope, even if passed over 
porters 3 or 3^ feet high, commonly trails by far the major part 
of its length along the ground. Now, it appears from the dyna- 
mometer experiments of Mr. J. F. Harrison, C.E., and Mr. J. C. 
!Morton, in May and June last, that a very considerable propor- 
tion of motive-power may be sacrificed by imperfectly carrying 
the rope. The draught of 440 yards of Mr. Smith's rope, wholly 
dragging upon the ground, and passing round three pulleys, was 
3 cwts. — equal to about half the weight of the rope ; and the 
draught of 700 yards of Mr. Fowler's rope, wholly diagging on 
the ground, and passed round the clip-drum and one pulley, was 
cwts. — equal to more than one-third the weight of the rope. 
VVhen imperfectly carried upon rope-porters, the draught was 
diminished nearly one-half ; and when the rope was held clear 
from contact with the ground, the draught was only £- of a 
cwt. — only a sixth of the draught when trailing its full length. 
Hence we learn that, in dealing with fields of tolerable size, 3 or 
4 cwts. of draught (representing, at a pace of 3^ miles per hour, 
3 or 4 mechanical horse-power) may be wasted from not carrying 
the rope at all ; while there may be a difference of 2 or more 
horse-power between partially and perfectly supporting the rope 
above the land. The necessary tightening of the slack rope 
might be effected by applying a brake to the paying-out drum, 
but it Avould be very undesirable to do this. It was found in the 
aforesaid experiments that, while the draught of a certain length 
of the Woolston rope (running over porters at intervals of 20 to 
40 yards) was 2f cwts. when the slack drum ran loose, it was 
only 2 cwts. with the brake applied as usual: so that partial 
braking is an advantage. When the brake, however, was pressed 
so hard as to keep the slack rope entirely off the ground, the 
draught rose to 4 cwts. A simple brake, then, while saving a 
slight amount of power, as commonly used, would involve a 
great loss by friction, if employed to hold up the rope completely. 
Accordingly Messrs. Howard adopt a method of returning to the 
pulling rope a portion of the strain which retards the slack or 
outgoing rope. At a few yards' distance from the windlass a 
compensating pulley, loosely hung between two fixed pulleys, 
pinches the hauling rope into the groove of one pulley, while at 
the same time pinching the slack rope into the groove of the 
other pulley — so that the outgoing slack rope helps to haul the 
pulling rope ; and while the pressure in this self-acting apparatus 
is pr()j)ortioned to the strain exerted by the windlass upon the 
hauling rope, there is no pressure at all when the rope is doing 
no work — thus enabling the portion of spare rope to pass freely 
to the windlass as the implement commences its journey. The 
