The little book Of which this is an enlarged version was first issued in 1901, and has passed through'a considerable number Of editions. From time to time I have been asked if it might not be possible to widen its scope without sacrifice of simplicity or essential change in the mode Of presentation. As my own teaching experience warranted me in considering this step both practicable and advisable, some four years ago I set about recasting the original book, but the revised issue, owing to war conditions, has been delayed until now.
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