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PHYSICS: C. BARUS 
maximum age are more apt to be males. Whatever of adaptational effect there 
may be detected in this arrangement is probably, however, not of great im- 
portance. The major share of the reproductive activity of the chiton popu- 
lation is carried on by individuals between five and seven years old; they are 
more numerous than the older ones, and the volume of the gonad is in them 
relatively greater than at other ages. The proportion of the sexes is here very 
nearly as 1:1. These animals are usually found close together in groups of a 
dozen or more, under stones or in crevices. 
5 i 5 6 f 6 3 70 // /a 
FIG. 4. VARIATIONS IN THE PROPORTION OF MALES IN DIFFERENT AGE-GROUPS OF CHITON 
TUBERCULATUS 
® = Great Sound; O = Cross Bay. 
Summary. — Curves have been derived which illustrate the extent to which 
the rate of growth and the duration of life of Chiton tuberculatus may be 
modified in differing natural environments at Bermuda; attention is also- 
called to variations found in the proportion of the sexes, in different year- 
groups. 
1 Contributions from the Bermuda Biological Station for Research, No. 97. 
2 Cf. Crozier, W. J., and Arey, L. B., Amer. Jour. Physiol., Baltimore, 46, 1918, (487-492). 
Arey and Crozier, (in press). 
3 Heath, H., Zool. Am., Leipzig, 32, 1907, (10-12). 
THE INTERFEROMETRY OF VIBRATING SYSTEMS 
By C. Barus 
Department of Physics, Brown University 
Communicated, September 6, 1918 
1. Introductory. — The high luminosity of the achromatic interferences and the- 
occurrence of but two sharp fringes, make it possible to utilize them even in 
cases when the auxiliary mirrors vibrate. Experiments of a similar kind were 
