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PREFACE.

I HAVE endeavoured in this book to give some account
-of the experiments on Positive Rays which have been
made at the Cavendish Laboratory during the last
seven years, and which have been the subject of papers
scattered through the Philosophical Magazine, the
Proceedings of the Royal Society, and the Proceedings
of the Cambridge Philosophical Society. I have, in
addition, included a short account of the researches of
Stark and others on the Doppler effect in Positive
Rays and of Gehrcke and Reichenheim's experiments
on Anode Rays, as these, those on the Doppler effect
especially, are very closely connected with the results
obtained by the very different methods described in the
earlier part of this book. I have described at some
length the application of Positive Rays to chemical
.analysis ; one of the main reasons for writing this book
was the hope that it might induce others, and especially
chemists, to try this method of analysis. I feel sure
that there are many problems in Chemistry which could
be solved with far greater ease by this than by any
other method. The method is surprisingly sensitive—
more so even than that of Spectrum Analysis, requires
,an infinitesimal amount of material, and does not require



	PREFACE. I HAVE endeavoured in this book to give some account -of the experiments on Positive Rays which have been made at the Cavendish Laboratory during the last seven years, and which have been the subject of papers scattered through the Philosophical Magazine, the Proceedings of the Royal Society, and the Proceedings of the Cambridge Philosophical Society. I have, in addition, included a short account of the researches of Stark and others on the Doppler effect in Positive Rays and of Gehrcke and Reichenheim's experiments on Anode Rays, as these, those on the Doppler effect especially, are very closely connected with the results obtained by the very different methods described in the earlier part of this book. I have described at some length the application of Positive Rays to chemical .analysis ; one of the main reasons for writing this book was the hope that it might induce others, and especially chemists, to try this method of analysis. I feel sure that there are many problems in Chemistry which could be solved with far greater ease by this than by any other method. The method is surprisingly sensitive— more so even than that of Spectrum Analysis, requires ,an infinitesimal amount of material, and does not require