Microscopical Light in Geological Darkness, — Clay pole, 223 
is "highly suggestive." But if we can realize the figures of 
some modern molecular physicists regarding space we can 
hardly entertain the suggestion, for they tell us that in the 
interplanetary regions there is only one molecule of any kind 
in 10^'* cubic miles of space. In such an absolute, awful 
solitude, the earth can surely not have been able to gather up 
the needed carbon-dioxide, though she had sought it from 
pre-Cambrian times down to the present day. 
But here the microscopist comes upon the field and offers 
his services in the cause of peace. In diplomatic language, 
he proposes to act as mediator. He points out, as I have 
already said, the minute cavities existing in the crystalline 
rocks and shows that in them is hidden a store of carbonic 
acid, hoarded, as it were, in the pockets of mother earth, in- 
finitesimally small but infinitely numerous, and he suggests 
that possibly here a source may be found from which the 
geologist may get his coal and the botanist his carbonic acid, 
without alarming the zoologist for the safety of his animals. 
He shows that on this view it is no longer necessary to as- 
sume its presence in the atmosphere all at the same time. In- 
stead of this he suggests that it may have been, and prob- 
ably was, set free almost atom by atom as the crystalline rocks 
yielded to erosion and these "sealed flasks" were, .one after 
another, burst open by the pressure within. 
At first blush we may be disposed to laugh at the sugges- 
tion and to deem such microscopical contributions of small 
comparative value when so vast a demand is made. But it 
is well to recollect that "many a little makes a mickle." Let 
us look at the matter quantitatively for a moment, for here 
must lie the crucial test. If our theory fails here it fails al- 
together, though if it pass this test its ultimate success is not 
hereby assured. 
Since the investigation by Mr. Sorby, to which I referred 
at the outset, little advance has been made until quite recently, 
when a stimulus was given to new experiments by the mar- 
velous discovery of argon in the atmosphere. ^ ue distin- 
guished chemists who were engaged in that most remarkable 
investigation turned their attention to the gases contained in 
various minerals, among which were those of the crystalline 
rocks. .\nd in a paper recently read before the Royal Society 
