PHYSICS: K.-L. YEN 
91 
1 Preliminary communication. 
2 The paper will appear shortly in Science, New York, N. S., 1918. All the precautions 
mentioned in this account were carefully observed in the present investigation. 
3 The methods previously used in studying the photosynthesis of aquatic plants are 
not as accurate as the one here described, nor do previous experiments afford the kind of 
data needed for our purpose. Cf. Blackman, F. F., and Smith, A. M., Proc. Roy. Soc, 
London, (B) 83, 1911, (389). 
4 All matching of shades was done under a 'Daylight' lamp, so that uniform conditions 
were assured throughout the experiments. Cf. Science, New York, N. S., 42, 1915, (764). 
A clear space was left in the tube below the Viva to facilitate comparison of colors. In 
any single experiment the buffer may be dispensed with by using as a standard the pink 
solution produced by the first exposure. The first exposure should be as short as is con- 
sistent with obtaining a definite standard. Experiments showed that the trace of alcoholic 
phenolphthalein had no injurious effect. 
5 In experiments on fresh water algae a small amount of sodium bicarbonate was added 
to the water. 
6 This acceleration is not due to the increase in the intensity of light as the sun gets higher 
for it was also observed when the experiments were started at noon. 
7 When the sea water is not changed during the experiment the curve rises more rapidly 
at first then bends over to the right as the supply of CO2 is used up. 
8 This is because the catalyst from the moment of its production is in solution. It is 
not analogous to a solid going into solution, which dissolves more slowly as the limit of solu- 
bility is approached. 
9 While respiration is in a sense the opposite of photosynthesis the steps in the process 
are apparently quite different from those found in photosynthesis. 
10 1, e., under the conditions of the present experiment, where the reacting substances 
are kept approximately constant in composition. 
11 Aquatic plants taken directly from ice-covered ponds in winter are found to possess 
but feeble photosynthetic power, though of a deep green color. 
12 The activation of substances by light is well known in photochemistry. 
13 /. Biol. Chem., New York, 21, 1917, (585); 22, 1917, (23). 
MOBILITIES OF IONS IN AIR, HYDROGEN, AND NITROGEN 
By Kia-Lok Yen 
Ryerson Physical Laboratory, University of Chicago 
Communicated by R. A. Millikan, January 21, 1918 
In spite of the great number of investigations devoted to gases the ques- 
tion whether an ion is a molecule or an atom carrying an elementary charge, 
or whether it is a number of neutral molecules clustering about a charge is 
not as yet definitely settled. Both the ' cluster' hypothesis, according to 
which an ion is conceived of as a unit elementary charge surrounded by a 
satellite of neutral molecules, and the ' small-ion' hypothesis, according to 
which an ion is conceived of as a single molecule carrying an elementary 
charge, explain equally well the phenomenon which first necessitated the 
former, and also the older, hypothesis; this phenomenon being the fact that 
the mobilities and the diffusion coefficients of the ions in gases are relatively 
