In the left-hand photograph the two pieces of paper exactly balance. The
balance used is very sensitive, and when the single word "atoms" has
been written with a lead pencil upon one of the papers the additional
weight is sufficient to depress one of the pans as shown in the second
photograph. The spectroscope will detect less than one-millionth of the
matter contained in the word pencilled above.]
[Illustration: _Reproduced by permission of X-Rays Ltd._
THIS X-RAY PHOTOGRAPH IS THAT OF A HAND OF A SOLDIER WOUNDED IN THE
GREAT WAR