penetrating opaque
substances has been made by Mr. George F. Kunz, of the American Museum
of Natural History. Mr. Kunz describes this experiment as follows:

"Radium bromide of three hundred thousand activity was placed in a
sealed glass tube inside a rubber thermometer-holder, which was tightly
screwed to prevent any emanation of any kind from passing through the
joints. This was placed under a heavy silver tureen fully one-sixteenth
of an inch in thickness; upon this were placed four copper plates, such
as are used for engraving; upon these a heavy graduated measuring-glass
10 cm. in diameter; this was filled with water to a depth of six inches.
A diamond was suspended in the water and immediately phosphoresced.
Whenever the tube of radium was drawn away more than two or three feet
the phosphoresce ceased; whenever it was placed under the tureen the
diamond immediately phosphoresced again. This experiment proves that the
active power of the radium penetrated the following substances:

"Glass in the form of a tube, sealed at both ends; the rubber
thermometer-holder; silver tureen; four copper plates; a glass vase or
measuring-glass one-quarter of an inch in thickness; three inches of
water. There is no previously known substance or agent, whether it be
even light or electricity, that possesses such wonderfully penetrative
powers."*5*

THE NATURE OF EMANATIONS FROM RADIO-ACTIVE BODIES

What, then, is the nature of these radiations? Are they actually
material particles hurled through the ether? Or are they like light--and
possibly the Roentgen rays--simply undulations in the ether? As yet this
question is an open one, although several of the leading investigators
have postulated tentative hypotheses which at least serve as a working
basis until they are either confirmed or supplanted. On one point,
however, there seems to be unanimity of opinion--there seems to be
little question that there are at least three different kinds of rays
produced by radio-active substances. According to Sir William Crookes,
the first of these are free electrons, or matter in an ultra-gaseous
state, as shown in the cathode stream. These particles are extremely
minute. They carry a negative charge of electricity, and are identified
with the electric corpuscles of Thompson. Rays of the second kind are
comparable in size to the hydrogen atom, and are positively electrified.
These are easily checked by material obstructions, although they re