When undertaking to prepare a new edition of this book I received
permission from the authors to "throw it into the form in which you think
it would be most useful at the present time." It was left to my discretion,
"What to use and what to omit." I have not found it necessary to avail
myself to any considerable extent of this latter permission. But as the
contents of the book were originally arranged the reader was ill-prepared
to appreciate the importance of the later research for want of introductory
matter explaining how it began, and how the early research led up to the
later investigation. I have therefore contributed an entirely new
preliminary chapter which will, I hope, help the reader to realise the
credibility of the results attained when the molecular forms and
constitution of the numerous bodies examined were definitely observed. I
have not attempted to revise the records of the later research in which I
had no personal share, so from the beginning of Chapter III to the end the
book in its present form is simply a reprint of the original edition except
for the correction of a few trifling misprints.

I have thus endeavoured to bring into clear prominence at the outset the
scientific value of the light the book sheds on the constitution of matter.
The world owes a debt to scientific men of the ordinary type that cannot be
over-estimated, but though they have hitherto preferred to progress
gradually, from point to point, disliking leaps in the dark, the leap now
made is only in the dark for those who will not realise that the progress
to be accomplished by means of instrumental research must sooner or later
be supplemented by subtler methods. Physical science has reached the
conception that the atoms of the bodies hitherto called the chemical
elements are each composed of minor atoms. Instrumental research cannot
determine by how many, in each case. Occult research ascertained the actual
number in some cases by direct observation and then discovered the law
governing the numbers in all cases, and the relation of these numbers to