Dilated or condensed, bright or obscure,

Can execute their aery purposes,

And works of love or enmity fulfil."

Milton.

LONGMANS, GREEN, AND CO.
39 PATERNOSTER ROW, LONDON
NEW YORK AND BOMBAY
1903

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PREFACE

The title of this little volume sufficiently explains its contents; it only remains to add that much of the text has already appeared from time to time in the form of popular articles in various magazines. It has, however, been carefully revised and considerably added to in parts where later researches have thrown further light upon the subjects dealt with.

G. C. FRANKLAND