368 JAMES WATT. 



possessing any figure, to give a clear idea of the mode of 

 action in this little apparatus ; still I will attempt it. 



When gas escapes in a certain direction from the vase 

 in which it is contained, this vase by means of reaction 

 will be inclined to move in a diametrically opposite 

 direction. The recoil of a gun loaded with gunpowder 

 is a similar agency ; the gas engendered by the combus- 

 tion of the saltpetre, the charcoal, and the sulphur, rushes 

 into the air according to the direction of the gun ; the 

 reaction, produced in the rear, reaches the shoulder of 

 the person who fires it ; it is on the shoulder then that 

 the recoil must act. To change the direction of the 

 recoil, it would suffice to make the jet of gas issue in 

 another direction. If the gun were closed at the end, 

 and were pierced only by a lateral opening horizontally 

 perpendicular to its direction, the gas from the powder 

 would escape laterally and horizontally ; therefore the 

 recoil would act perpendicularly to the direction of the 

 gun ; and its force would be exerted on the arms and 

 not on the shoulder. In the former instance, the recoil 

 pushed the man who fired from the front to the rear, as 

 if to upset him ; in the second instance it would tend to 

 turn him round on his own axis. Let the gun then be 

 invariably fixed, and horizontally, to a vertical movable 

 axis, and at the instant of being fired, it will alter its 

 direction more or less, and it will also make the axis turn. 



Continuing the same arrangements, let us suppose the 

 rotatory vertical axis to be hollow, but closed at its upper 

 end ; let it rise from the base as a sort of chimney from 

 the caldron where gas is engendered ; let there be 

 besides a free lateral communication between the inte- 

 rior of this axis and the interior of the gun's barrel, so 

 that, after having filled the interior of the axis, the steam 



