396 RECORD OF SCIENCE FOR 1887 AND 1888. 



where Cp and c/ designate respectively, the specific heats at constant 

 pressure of air and of non-saturated aqueous vapor; A=430, approxi- 

 mately, is the mechanical equivalent of a unit of heat. T and^) per- 

 tain to an initial state of the air, but Ti and j?i to a firal state. Bezold 

 gives a method of constructing by points an indefinite number of 

 adiabatics when we know one and when we have first constructed the 

 system of isotherms. 



In the dry stage the adiabatics are appreciably independent of a?, 

 which is a very small quantity, and they can be regarded as sensibly 

 the same as the adiabatics for dry air entirely without aqueous vapor. 



Resume. — For the dry stage the condition of the atmosphere is repre- 

 sented by three systems of lines that can be traced upon a diagram, 

 whose CO ordinates are^ audi?, which lines constitute a net- work inter- 

 secting each other over the whole plane of co-ordinates, as follows : 



(1 ) Isotherms that are equilateral hyperbolas that depend, respectively, 

 upon the values of the variable parameter T, but can for a given temp- 

 erature be considered as independent of x, the quantity of aqueous 

 vapor. 



(2) Lines of saturation, the position of each of which depends on the 

 variable parameter x. Each line of saturation divides the plane of co- 

 ordinates into two parts; on the concave side of this curve the dry 

 stage is represented, and on the convex side the wet stage. 



(3) Adiabatics, which are asymptotic to the axes of jp and v and inter- 

 sect the two preceding systems of lines ; these adiabatics are sensibly 

 tlie same as those that relate to -absolutely dry air. 



(C.) THE RAIN STAGE.— When rain is forming let x be the quantity of 

 saturated vapor that is associated with one kilogram of dry air, and x' 

 the quantity of water as such suspended within this kilogram of dry 

 air ; let M be the mass of the mixture ; we have the equation 



M=l+x-fx' 



Here the tension of the vapor is determined by the temperature it- 

 self; if e designates this tension then we have the two following equa- 

 tions of condition as representing the relations in this stage of rain : 



i>=RAj+^ (C) 



c=a?R. - (7) 



"v 



The following remarks may be made with regard to the rain stage : 

 (1) The quantity of water in suspension, x', is always very small ; for 

 as soon as this quantity becomes rather large the water separates from 

 the foggy mass and falls ; therefore the changes of condition are irre- 

 versible. • 



