751 
of Edinburgh, Session 1871-72. 
Boulders of large size on top of Applecross Hills. Rocks 
below, striated. Direction of striae S. 20° W. (true.) (Re- 
porter — Nicol of Aberdeen.) 
Wigtownshire. 
Olasserton . — Granite boulder, 9x6x6 feet, about 24 tons. Longer 
axis N.E. Two small boulders to east of above, and in a line 
with it. These boulders supposed to have come from moun- 
tains to N.E., across arm of sea. Kaims in parish, full of 
granite pebbles. (Reporter — Archibald Stewart.) 
The following Gentleman was elected a Fellow of the 
Society : — 
Thomas B. Christie, M.D., F.R.C.P.E. 
Monday , §th May 1872. 
D. MILNE HOME, LL.D., Vice-President, in the Chair. 
The following Communications were read : — 
1. On the Chemical Efficiency of Sunlight. 
By James Dewar, Esq. 
Of all the processes proposed to measure varying luminous in- 
tensities by means of chemical effects, not one has yet been 
expressed in strictly dynamical measure. This is owing to the 
very small amount of energy to be measured necessitating very 
peculiar processes for its recognition. The chemical actions gene- 
rally induced by light are of the “Trigger” or “Relay” description ; 
that is, bear no necessary relation to the power evolved by the 
transformation. There is one natural action of light continuously 
at work of a very different kind in the decomposition of carbonic 
acid by plants, necessitating a large absorption of energy, and thus 
enabling us to ascertain the proportion of the radiant power 
retained, through the chemical syntheses effected. 
So far as I am aware, the following passage extracted from 
Helmholtz’s Lectures “On the Conservation of Energy,” delivered 
