226 II. JT. Davis — Colors by Transmitted Light. 



ing — very rapidly at first — and the latter increasing as t 

 increases). This formula is, of course, a rough approximation, 

 but analogies between it and v*=2gs 'are very interesting. 

 These " drops " are not simply bulges due to variations in the 

 surface tension of a film (for similar phenomena appear in the 

 image of a thin glass cell filled with solution) but are little 

 globules floating in the liquid, composed of a more concentrated 

 solution with greater density and refracting power, and with 

 a surface tension with respect not only to air but to the rest of 

 the solution ; though the process by which such definitely 

 separated globules are formed is not quite clear. 



It is not unlikely that further study of the nature, form, and 

 velocity of such descending masses, both in films and in thin 

 cells (where they are spheres and the surrounding medium is 

 stationary) may lead to a method of investigation not only of 

 changes in viscosity due to evaporation but possibly also of the 

 problems of surface-viscosity, in connection with which further 

 knowledge would be very desirable. 



Brown University, Providence, R. I. 



