238 THE EVOLUTION OF LIFE 
allude to the question of the desirability or the 
reverse of employing, in these experiments, kinds of 
glass which, like rock-crystal, are much more per- 
vious to actinic rays of light than ordinary soft or 
hard German glass. I have made a few observa- 
tions with sealed tubes composed of uviol glass, 
which is said to possess such properties, but they 
have not been numerous enough to enable me to 
say that their use has favoured the appearance of 
organisms or the reverse. The specimens of 
such glass at present obtainable! have proved very 
variable in texture, and this led to several explosions 
occurring when the sealed tubes had been heated to 
temperatures over 130 C. Further experiments 
with glass vessels of this kind should, however, be 
made ; though perhaps the advantage to be derived 
therefrom will not be so great as might at first be 
imagined, if what M. Wilderman says is substanti- 
ated by further observations. He states that he 
is prepared with ‘‘experimental proof that the rays 
of light of all wave lengths act both ‘chemically’ and 
as ‘heat-rays,’ only in different degrees.” ? 
Of late, however, all the experimental vessels that 
I have been exposing to diffuse daylight have been 
laid on a table in front of an open window (day and 
night) having a north-east aspect; the table being 
so disposed as not to be touched by the rays of the 
early morning sun. In this way the window glass 
at least does not come as an additional barrier to the 
passage of actinic rays, while the commonly reputed 
1 Through Messrs Isenthal & Co., of 85 Mortimer Street, W. 
2 Proceedings of Royal Society, A, March 1906, p. 274. 

