HISTORY OF THE ATOMIC THEORY. 37 



The four laws given by him are — 



" 1. When two elastic fluids, denoted by A and J3, are 

 mixed together, there is no mutual repulsion amongst their 

 particles ; that is, the particles of A do not repel those of B, 

 as they do one another. Consequently, the pressure or 

 whole weight upon any one particle arises solely from those 

 of its own kind. 



" 2. The force of steam from all liquids is the same, at equal 

 distances above or below the several temperatures at which 

 they boil in the open air ; and that force is the same under 

 any pressure of another elastic fluid as it is in vacuo. Thus 

 the force of aqueous vapour of 212° is equal to 30 inches of 

 mercury; at 30° below, or 182°, it is of half that force; and 

 at 40° above, or 252°, it is of double the force ; so likewise 

 the vapour from sulphuric ether, which boils at 102°, then 

 supporting 30 inches of mercury, at 30° below that tem- 

 perature it has half the force, and at 40° above it, double 

 the force; and so in other liquids. Moreover the force of 

 aqueous vapour of 60° is nearly equal to J inch of mercury, 

 when admitted into a Torricellian vacuum ; and water of the 

 same temperature, confined with perfectly dry air, increases 

 the elasticity to just the same amount. 



" 3. The quantity of any liquid evaporated in the open air 

 is directly as the force of steam from such liquid at its tempe- 

 rature, all other circumstances being the same. 



"4. All elastic fluids expand the same quantity by heat; 

 and this expansion is very nearly in the same equable way as 

 that of mercury ; at least from 32° to 212°. It seems probable 

 the expansion of each particle of the same fluid, or its sphere 

 of influence, is directly as the quantity of heat combined 

 with it ; and consequently the expansion of the fluid as the 

 cube of the temperature, reckoned from the point of total 

 privation." 



The first law accounts for a diff'usion of gases to a great 

 extent, but not entirely. It would result from it, if not qua- 



