What is "whip purchase"

Whip \Whip\, n. [OE. whippe. See Whip, v. t.]

1. An instrument or driving horses or other animals, or for correction, consisting usually of a lash attached to a handle, or of a handle and lash so combined as to form a flexible rod. ``[A] whip's lash.''
   --Chaucer.

   In his right hand he holds a whip, with which he is supposed to drive the horses of the sun.
   --Addison.

2. A coachman; a driver of a carriage; as, a good whip.
   --Beaconsfield.

3. (Mach.)

   1. One of the arms or frames of a windmill, on which the sails are spread.

   2. The length of the arm reckoned from the shaft.

4. (Naut.)

   1. A small tackle with a single rope, used to hoist light bodies.

   2. The long pennant. See Pennant (a)

5. A huntsman who whips in the hounds; whipper-in.

6. (Eng. Politics)

   1. A person (as a member of Parliament) appointed to enforce party discipline, and secure the attendance of the members of a Parliament party at any important session, especially when their votes are needed.

   2. A call made upon members of a Parliament party to be in their places at a given time, as when a vote is to be taken.

7. A whipping motion; a thrashing about; as, the whip of a tense rope or wire which has suddenly parted; also, the quality of being whiplike or flexible; flexibility; suppleness, as of the shaft of a golf club.

8. (Mech.) Any of various pieces that operate with a quick vibratory motion, as a spring in certain electrical devices for making a circuit, or a rocking certain piano actions. Whip and spur, with the utmost haste. Whip crane, or Whip purchase, a simple form of crane having a small drum from which the load is suspended, turned by pulling on a rope wound around larger drum on the same axle. Whip gin. See Gin block, under 5th Gin. Whip grafting. See under Grafting. Whip hand, the hand with which the whip is used; hence, advantage; mastery; as, to have or get the whip hand of a person. --Dryden. Whip ray (Zo["o]l.), the European eagle ray. See under Ray. Whip roll (Weaving), a roll or bar, behind the reeds in a loom, on which the warp threads rest. Whip scorpion (Zo["o]l.), any one of numerous species of arachnids belonging to Thelyphonus and allied genera. They somewhat resemble true scorpions, but have a long, slender bristle, or lashlike organ, at the end of the body, instead of a sting. Whip snake (Zo["o]l.), any one of various species of slender snakes. Specifically:

   1. A bright green South American tree snake ( Philodryas viridissimus) having a long and slender body. It is not venomous. Called also emerald whip snake.

   2. The coachwhip snake.