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51.

DISCOURS III
of ye equilibrium of fluid bodys by ye shock

Flame can make an equilibrium by its shock with weights, we may measure its force, if letting it go out of a pipe sufficiently large it dogheth against ye winges at a wheel situated horizontally, provided that these wings are situated obliquely in ye same manner as those of wind=mills.  In many places ye flame wch mounts up ye chimnys [[?serves]] to turn some small engines near ye fire;  ye greater ye fire ye swifter ye motion of ye flame:  But that motion cannot be augmented much by art, and its shoc hath not much force;  a flying squib is elevated by ye shoc of its flame against ye air, but if it weighs much it cannot be elevated so we may measure its equilibrium.  Ye flame of thunder wch goeth very swift maketh very considerable efforts:  for it over turns towns and rocks, ye swiftness of ye flame increaseth also ye force of ye burning, as is often observed in great fires when ye wind is great.  We see also very considerable effects when ye enamillers blow ye fire of their lamps against glass or against mettals to melt them:  but because that ye flame is not easily governed to remain of ye same largeness and swiftness, at that it would cost much to maintain it, these engines are rarely made use of;  it is not therefore necessary to examine its force in this place now to compare it with that of other fluid bodys:

  The air and water are employed in engines to move them by their shock.  We may know ye equilibrium that is made between waters and with firm body they dash against by ye following rules:

RULE I
  The spouts of water do not shock by ye effort of all their parts as ye firm body do.

Explication:

[[images:  Vertical cylinder labeled C (top), D (bottom); water flowing horizontally A d B to the right out of A D at D;  smaller horizontal cylinder (not attached to A D)labeled E F]]

A B is a spout of water going out of ye cylinder C D and E F is a cylinder of wood;  it is manifest that ye parts wch compose E F being linked and united together make there effort altogether in dashing against a body by ye extremity F;  but a spout of water A B being carried according to ye direction A d B, canot act by its first parts:  for ye water being fluid and as it were composed of an infinite number of small corpuscules wch glide one upon ye other;  as to ye small grains of sand it is but ye first towards B, wch can make ye first effort upon ye bodys they incounter, and they are as [[ind?]] have dashed in their turn.  To understand it we must consider that ye swiftness that ye water hath at ye going out of a small hole made at ye bottom of a large pipe is very different from ye swiftness of that wch goeth though a pipe of an equal largeness thrô out:  for as much as in ye last case ye water begins to go out with a very small swiftness and like to that of a cylinder of ice which we permitt to fall:

Transcription Notes:
mandc: Squib: a small firework that burns with a hissing sound before exploding.