. 141. Nickel-plating.

142. Miscellaneous Notes on Electroplating.

Sec. 143. Blacking Brass Surfaces.

Sec. 144. Sieves.

Sec. 145. Pottery making in the Laboratory.

APPENDIX.

PLATINISING GLASS.

PREFACE

EXPERIMENTAL work in physical science rests ultimately upon the
mechanical arts. It is true that in a well-appointed laboratory,
where apparatus is collected together in greater or less profusion,
the appeal is often very indirect, and to a student carrying out a set
experiment with apparatus provided to his hand, the temptation to
ignore the mechanical basis of his work is often irresistible.

It often happens that young physicists are to be found whose
mathematical attainments are adequate, whose observational powers are
perfectly trained, and whose general capacity is unquestioned, but who
are quite unable to design or construct the simplest apparatus with
due regard to the facility with which it ought to be constructed.
That ultimate knowledge of materials and of processes which by long
experience becomes intuitive in the mind of a great inventor of course
cannot be acquired from books or from any set course of instruction.

There are, however, many steps between absolute ignorance and
consummate knowledge of the mechanical arts, and it is the object of
the following pages to assist the young physicist in making his first
steps towards acquiring a working knowledge of "laboratory arts."
However humble the ambition may be, no one can be more keenly alive
than the writer to the inadequacy of his attempt; and it is only from
a profound sense of the necessity which exists for some beginning to
be made, that he has had the courage to air his views on matters about
which there are probably hundreds or thousands of people whose
knowledge is superior to his own.

Moreover, nothing has been further from the writer's mind than any
idea of "instructing" any one; his desire is--if happily it may so
befall--to be of assistance, especially to young physicists or
inventors who wish to attain definite mechanical ends with the minimum
expenditure of time. Most people will agree that one condition
essential to success in such an undertaking is brevity, and it is for
this reason that alternative methods as a rule have not been given,
which, of course, deprives the book of any pretence to being a
"treatise." The writer, therefore, is responsible for exercising a
certain amount of discretion in the selectio