Preface to the Second Edition.
Since the first edition of this work appeared, in 1855, the manufacturing corporations at Lowell, lessees of the water-power furnished by the Merrimack River at that point, have surrendered their leases and taken others containing new provisions for the purpose of more fully protecting all parties in the enjoyment of their respective rights; this has rendered necessary a new and elaborate series of experiments for the purpose of perfecting the method of gauging the flow of water in open channels by the use of loaded tubes. Some experiments had been made on this subject at Lowell before the publication of the first edition, the principal results of which were given; the later experiments are, however, so much more complete, and have been made under circumstances so much more favorable, that it has been found necessary to rewrite, entirely, the chapter on that subject.
The general use at Lowell of the Diffuser, an apparatus for utilizing the power usually lost in turbines, from the water leaving them with a considerable velocity, has created much interest in Venturi's tube, the action in which involves the same principles as the Diffuser. Experiments on Venturi's tube had been previously made only when discharging into the air; it appeared highly probable that greater results might be obtained if the tube was submerged, so as to discharge under water. Experiments made under these circumstances, and detailed at length in this edition, indicate a considerably greater flow than had been previously obtained.
The author takes this opportunity of acknowledging his obligations to Mr. Uriah A. Boyden of Boston, for useful suggestions during the last twenty-five years, on almost every subject discussed in this volume. Also to Mr. John Newell, now of Detroit, Michigan, to whom he is much indebted for assistance in the execution and reduction of some of the most important series of experiments, and to whose fidelity the precision attained in the results is in no small degree due. Also to Mr. Joseph P, Frizell, now of Davenport, Iowa, to whom he is indebted for assistance in some points involving the higher mathematics.
Lowell, Mass., March, 1868.
