93 
of the upper shelf and regarded with new interest. In a day it had ceased 
to be a forgotten, though curious, plaything, and had become a powerful 
instrument of research. It was before Roentgen’s discovery that a well- 
known professor said to me that he considered it foolish for one to spend 
any part of his departmental appropriation for a vacuum; that when he 
paid out money he wanted something in return—not an empty space. And 
yet this man was familiar with the work of Faraday and of Crookes, both 
of whom with prophetic mind had foreseen and foretold. Let me quote 
from a lecture by Faraday on the significant subject “Radiant Matter.” 
1“T may now notice a peculiar progression in physical properties (of 
matter) accompanying changes of form, and which is perhaps sufficient to 
induce, in the inventive and sanguine philosopher, a considerable degree 
of belief in the association of the radiant form with the others in the 
set of changes I have mentioned. 
“As we ascend from the solid to the fluid and gaseous states, physical 
properties diminish in number and variety, each state losing some of those 
which belong to the preceding state. * * * The varieties of density, 
hardness, opacity, color, elasticity and form, which render the number of 
solids and fluids almost infinite, are now supplied by a few slight varia- 
tions in weight and some unimportant shades of color. 
“To those, therefore, who admit the radiant form of matter, no difficulty 
exists in the simplicity of the properties it possesses * * * , They point 
out the greater exertions which nature makes at each step of the change 
and think that, consistently, it ought to be greatest in the passage from 
the gaseous to the radiant form.” The lecture from which the foregoing 
is a quotation was delivered in 1816, when Faraday was but twenty-four 
years old. 
Let me quote again, this time from a lecture by Sir William Crookes 
delivered sixty years later, more than thirty years ago, on the same sub- 
ject—“‘Radiant Matter.” 
“In studying this fourth state of matter we seem at length to have 
within our grasp and obedient to our control the little indivisible particles 
which with good warrant are supposed to constitute the physical basis of 
the universe. We have seen that in some of its properties radiant matter 
is aS material as this table, whilst in other properties it almost assumes 
the character of radiant energy. We have actually touched the borderland 
where matter and force seem to merge into one another, the shadowy realm 
1Life and Letters of Faraday, Vol. 1, p. 308. 
