396 
Proceedings of the Boy at Society 
in the green cells of Vortex viridis. I hope, however, shortly to 
figure these cells and the spectrum of their chlorophyll. 
I consider that experiment upon the living organism by exposure 
to sunlight is not only the best, but the only absolutely safe and 
certain way of recognising any pigment as chlorophyll. And the 
entire absence of any evolution of gas from Bonellia, Idotea , and 
various other green animals (p. 379), disproves, at any rate, the 
extreme form in which Pringsheim’s “ screen ” theory is sometimes 
stated, although, as Lankester points out, and as Pringsheim 
doubtless intends, it is more probable that it should only be applied 
to true chlorophyll. 
H. I have omitted in the body of the paper to call attention to 
the great importance of consortism in the economy of nature, for, 
since the Radiolarians, and doubtless also, at least to a large 
extent, the Foraminifera, are thus chiefly maintained, and since 
they serve as nutriment directly or indirectly to most of the higher 
pelagic animals, the apparently disproportionate abundance of 
animal life in the open sea becomes no longer enigmatical. 
2. On the Thermodynamic Acceleration of the Earth’s 
Rotation. By Sir William Thomson. 
It has long been known, having been first, I believe, pointed out 
by Kant, and more recently brought very near to a practical conclu- 
sion by Delaunay, that the earth’s rotational velocity is diminished 
by tidal agency, in virtue of the imperfect fluidity of the ocean. 
An integral effect of all the consumption of energy by fluid friction 
(or more properly speaking by continued deformation of fluid 
matter) in the tidal motions, is to cause the time of high water on 
an average for the whole earth to be not exactly either transit, or 
6 o’clock, as it would be were the ocean a perfect fluid, but to be 
some time after transit, and before 6 o’clock.* Thus we may 
* For brevity, I use tlie word “ transit” to denote a time of transit of tbe tide- 
generating body (whether sun or moon), or a time of transit of the point of 
the heavens opposite to the tide-generating body, across the meridian of the 
place ; and the word 6 “o’clock, ” to denote the middle instant of the interval of 
time between consecutive transits, If, to fix the ideas, we first think of the 
