450 THE POPULAR SCIENCE MONTHLY 
man effect, 1896; radium, 1898; atomic disintegration, the transforma- 
tion of matter, the thermal effect of radioactivity, and intra-atomic 
energy, 1903. I am unable to locate the sixth decimal idea in recent 
catalogues. 
J. J. Thomson likens the discovery of Rontgen rays to the discovery 
of gold in a sparsely populated country. Workers come in large num- 
bers to seek the gold, many of them finding that “the country has 
other products, other charms, perhaps even more valuable than the gold 
itself.” 
The chief value of Réntgen’s discovery was not that it furnished 
us a “new kind of light for the investigation of dark places,” but in the 
fact that it led a host of workers to study vacuum-tube discharges—the 
discharge of electricity in gases and the effects of such discharges on 
matter itself. The old dusty Crookes tube was taken down from the far 
corner 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 Rontgen’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.” ? 
I 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 proper- 
ties 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 variations in weight and some unim- 
portant 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 twenty years ago, on the same sub- 
ject —“ Radiant Matter.” 
2“ Life and Letters of Faraday,” Vol. I., p. 308. 
