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72. the most interesting of the applications of steam-power, to the political economist and to the historian, as well as to the engineer, is its use in ship-propulsion.

In the modern marine engine we find one of the most important adaptations of steam machinery and the greatest of all the triumphs of the mechanical engineer.

Although, as has been already stated in previous lectures, attempts had been made, before the beginning of the present century, to successfully effect this application of the power of steam, they did not succeed, in any instance, as commercial enterprises, until after that date.

Indeed, it is but a few years ago that the passage across the Atlantic was made by sailing-vessels almost exclusively, and that the dangers, the discomforts, and the irregularities of their trips were most serious.

Now, hardly a day passes that does not see several large and powerful steamers leaving the ports of New York and Liverpool to make the same voyages; and their passages are made with such regularity and safety that travelers can anticipate, with confidence, the time which will mark the termination of their voyage, predicting the day and almost the hour of their arrival, and can cross with safety and comparative comfort, even amid the storms of winter.

Yet, all that we to-day see of the extent and the efficiency of steam-navigation has been the work of the present century; and it may well excite both our wonder and our admiration.

73. The history of this development of the use of steam-power illustrates, more perfectly than any other, that process of the growth of this invention which has been already referred to. We can here trace it, step by step, from the earliest and rudest devices up to those most recent and most perfect designs, which represent the most successful existing types of the heat-engine—whether considered with reference to its design and construction, or as the highest application of known scientific principles—that have yet been found attainable in even the present advanced state of the mechanic arts.

74. This application of the force of steam was very possibly