August 4, 1911] 



SCIENCE 



153 



ing upon each other, some are carried into the 

 water by their own velocity and some are 

 thrown into the water by the force of the 

 blows received from other molecules, thus de- 

 creasing the number in the vapor and allow- 

 ing others to escape from the water. When 

 the number that escape and the number that 

 are carried and thrown back into the water 

 equal each other a condition of equilibrium is 

 established and the space is said to be sat- 

 urated. 



If the temperature of the space or the vapor 

 within the space now be raised, what will 

 happen ? 



The molecules of vapor at a temperature of 

 40° F. have a given velocity and amplitude of 

 motion. The increase of the temperature 

 from 40° to 50° increases their velocity and 

 movement, and to exercise this increased 

 activity requires more space. We, therefore, 

 are accustomed to say that the vapor expands 

 or increases in volume when its temperature 

 is raised. In expanding some of the vapor 

 overflows the original space, and the number 

 of molecules within the space is thus decreased 

 by the number that has been crowded out of 

 the cylinder. This destroys the condition of 

 equilibrium and permits the molecules at the 

 surface of the water to escape again in greater 

 numbers. Thus, the process of evaporation 

 continues, establishing finally as before a con- 

 dition of equilibrium at the new temperature 

 of 50° F. This is our understanding, why 

 increased temperature gives increased capacity 

 when the vapor is free to expand, except for 

 the control of gravity. But if we put a lid 

 on the cylinder and thus confine the vapor to 

 a definite space we limit the field of its activity 

 but not the activity itself. The eif ort of vapor, 

 humidity, steam, water gas — whatever name 

 we may use to designate it — to obtain more 

 space increases with its temperature whether 

 confined within a limited space or not. If the 

 space is limited the effect is increased pres- 

 sure; if not limited increased volume. In 

 either case it obeys the laws of gases. The 

 only difference between atmospheric moisture 

 and steam is that the activities of the former 

 are limited by gravity alone, while the activi- 



ties of the latter are confined to a definite 

 space. WiLFOED M. Wilson 



Cornell University 



a variant in the periodical cicada 



While collecting material for a study of 

 the mode of pigment formation in the period- 

 ical cicada (Tihicen septendecim L.) my at- 

 tention was attracted by an adult male in 

 whose eyes the red pigment was lacking. The 

 specimen was secured at Summit, N. J., on 

 June 6, and although the cicadas occurred 

 there in countless thousands I searched in 

 vain for a second specimen. 



The example secured difi^ered from the 

 usual form not only in lacking the red pig- 

 ment of the eyes, which in this specimen are 

 perfectly white, but also in the coloration of 

 the wing veins. In this individual the costa 

 of the fore wings and the costa and the greater 

 portion of the radius and media of the hind 

 wings lack the typical orange coloration and 

 are perfectly colorless. 



Morgan^ has recently caused white-eyed 

 mutants to occur in DrosopMlia by closely 

 inbreeding and it may be that this specimen 

 originated in the same manner if we assume 

 that the entire colony is descended from one 

 pair of cicadas. A study of the inheritance 

 of this trait would be very interesting, but 

 such a study is obviously impracticable owing 

 to the long period of adolescence. 



Eoss Aiken Gortner 



Station for Experimental Evolution 



QUOTATIONS 

 tripped by red tape 



That the Department of Agriculture 

 should be in danger of losing three of its 

 leading experts on food adulteration, Wiley, 

 Bigelow and Eusby, on account of a tech- 

 nical violation of the salary regulations, 

 shows how a government is hampered by its 

 bureaucratic methods. It is not claimed that 

 Professor Eusby, of Columbia University, 

 was avaricious in refusing to work for $9 a 

 day or that the departmental authorities who 

 arranged for him to be paid at the rate of 



'Morgan, Science, N. S., XXXIIL, No. 849, 

 p. 534, April 7, 1911. 



