angle. The X-ray will not reflect, but instead, pass directly through
the glass.

Then, ordinary light is capable of refraction. This is shown by a ray of
light bending as it passes through a glass of water, which is noticed
when the light is at an angle to the surface.

The X-ray will pass through the water without being changed from a
straight line. The foregoing being the case, it was but a simple step to
conclude that if it were possible to find a means whereby the human eye
could see within the ultra-violet beam, it would be possible to see
through opaque substances.

From the discovery so important and far reaching it was not long until
it was found that if the ultra-violet rays, thus propagated, were
transmitted through certain substances, their rates of vibration would
be brought down to the speeds which send forth the visible rays, and now
the eye is able to see, in a measure at least, what the actinic rays
show.

This discovery was but the forerunner of a still more important
development, namely, the discovery of _radium_. The actual finding of
the metal was preceded by the knowledge that certain minerals, and
water, as well, possessed the property of radio-activity.

Radio-activity is a word used to express that quality in metals or other
material by means of which obscure rays are emitted, that have the
capacity of discharging electrified bodies, and the power to ionize
gases, as well as to actually affect photograph plates.

Certain metals had this property to a remarkable degree, particularly
uranium, thorium, polonium, actinium, and others, and in 1898 the
Curies, husband and wife, French chemists, isolated an element, very
ductile in its character, which was a white metal, and had a most
brilliant luster.

Pitchblende, the base metal from which this was extracted, was
discovered to be highly radio-active, and on making tests of the product
taken from it, they were surprised to find that it emitted a form of
energy that far exceeded in calculations any computations made on the
basis of radio-activity in the metals hitherto examined.

But this was not the most remarkable part of the developments. The
energy, whatever it was, had the power to change many other substances
if brought into close proximity. It darkens the color of diamonds,
quartz, mica, and glass. It changes some of the latter in color, some
kinds being turned to brown and others into violet or purple tinges.

Radium has the capacit