m. 4-949300 

 4-964658 

 4-859748 

 6-117662 

 6012752 

 8-276025 



640 Mr. Rankine on the Centrifugal Theory of Elasticity, 



The following are some additional values of the constant a for 

 steam, corresponding to various units of pressui*e used in prac- 

 tice : — 



Units of pressure. Values of a. 



Atmospheres of 760 millimetres of mercury — 



= 29*922 inches of mercury 



= 14*7 lbs. on the square inch 



= 1-0333 kilog. on the square centim. 4-950433 

 Atmospheres of 30 inches of mercury — 



= 761-99 millimetres 



= 14-74 lbs. on the square inch 



= 1-036 kilog. on the square cent 

 Kilogrammes on the square centimetre 

 Kilogrammes on the circular centimetre . 

 Pounds avoirdupois on the square inch 

 Pounds avoirdupois on the circular inch , 

 Pounds avoirdupois on the square foot 



All the numerical values of the constants are for common 

 logarithms. 



(35.) According to the principles which form the basis of cal- 

 culation in this section, every substance, in the solid or liquid 

 state, is surrounded by an atmosphere of vapour, adhering to its 

 surface by molecular attraction ; and even when the presence of 

 vapour is imperceptible at all visible distances from the body^s 

 surface, the elasticity of the strata close to that surface may be 

 considerable, and sufficient to oppose that resistance to being 

 brought into absolute contact, which is well known to be very 

 great in solid bodies, and perceptible even in drops of liquid. It 

 is possible that this may be the only cause which prevents all 

 solid bodies from cohering when brought together. 



The action of an atmosphere of vapour, so highly dense and 

 elastic as to operate at visible distances, may assist in producing 

 the spheroidal state of liquids. 



If the particles of clouds are small vesicles or bubbles (which 

 is doubtful), the vapour within them may, according to these 

 principles, be considerably more dense than that which pervades 

 the external air, and may thus enable them to preserve their 

 shape. 



Section VI. Of Mixtures of Gases and Vapours of different 



kinds. 



(36.) The principle stated in Section II. article 11, that the 

 elasticity of the atomic atmosphere is proportional to its density, 

 might be otherwise expressed by saying, that the elasticity of any 

 number of portions of atomic atmosphere, compressed into a given 

 space, is equal to the sum of the elasticities which such portions 

 would respectively have, if they occupied the same space separately. 



