Preface to the Second Edition
The first edition of this report having been exhausted in a few months and without satisfying the demand which the importance of the subject created, a second was ordered by Congress in March, 1879. The authors were thus given an opportunity to revise their text and eliminate a few formal errors which had crept in by reason of their absence while the first edition was passing through the press. The substance of the report is unchanged.
J. W. P.
July, 1879.