NOTE BY TRANSLATORS
The present is an abridged version of Prof. Knapp's book. For reasons of cost the translation has been confined for the present to the theoretical part; and Prof. Knapp’s illustrations have been considerably abridged, while every effort has been made to preserve his essential arguments.
To show the scope of the whole book, translated and untranslated, we have given the “Contents” in the complete form, including Chapter IV and the Appendices, which are here omitted.
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