n as to the production of those "flat"
surfaces for which he is so justly famous.

The writer is also indebted to Mr. A. E. Kennelly for some
information as to American practice in the use of insulating material
for electrical work, and to his friends Mr. J. A. Pollock and Dr. C.
J. Martin for many valuable suggestions. For the illustrations
thanks are due to Mrs. Threlfall and Mr. James Cook. With regard to
matters which have come to the writer's knowledge by his being
specifically instructed in them from time to time, due acknowledgment
is, it is hoped, made in the text.

With regard to the question as to what matters might be included and
what omitted, the general rule has been to include information which
the author has obtained with difficulty, and to leave on one side that
which he has more easily attained. All the "unities" have been
consistently outraged by a deliberate use of the English and metric
systems side by side. So long as all the materials for mechanical
processes have to be purchased to specifications in inches and feet,
it is impossible to use the centimetre consistently without
introducing inconvenience. However, everybody ought to, and probably
does, use either system with equal facility.

No attempt has been made at showing how work can be done without
tools. Though, no doubt, a great deal can be done with inferior
appliances where great economy of money and none of time is an object,
the writer has long felt very strongly that English physical
laboratory practice has gone too far in the direction of starving the
workshop, and he does not wish, even indirectly, 'to give any
countenance to such a mistaken policy. Physical research is too
difficult in itself, and students' time is too valuable, for it to be
remunerative to work with insufficient appliances.

In conclusion, the writer would ask his readers to regard the book to
some extent as tentative, and as a means to the procuring and
organising of information bearing upon laboratory arts. Any
information which can be given will be always thankfully received, and
the author hereby requests any reader who may happen to learn
something of value from the book to communicate any special
information he may possess, so that it may be of use to others should
another edition ever be called for.

CHAPTER I

HINTS ON THE MANIPULATION OF GLASS AND ON GLASS-BLOWING FOR LABORATORY
PURPOSES

Sec. 1. THE art of glass-blowing has the con