Page:Lectures on Ten British Physicists of the Nineteenth Century.djvu/42

 colleague, Sir William Thomson was so educated, and has all his life been an enthusiastic advocate of the metric system.

When one sails up the river Clyde towards Glasgow, he sees on either bank a long succession of shipbuilding yards. Glasgow was in Rankine's time famous for its naval architects and shipbuilders, and they were Rankine's special friends. Hence, he was led into a number of investigations which are of importance in navigation. One of his papers is on the exact form of waves near the surface of deep water, and another investigates the lines of motion of water flowing past a ship. M. Napier, a naval architect, asked him to estimate the horsepower necessary to propel at a given rate a vessel which he was about to construct; and supplied him in confidence with the results of a great number of experiments on the horsepower required to propel steamships of various sizes and figures at various speeds. Rankine deduced a general formula, which he communicated to Napier directly and to the world at large in the form of an anagram: 20A. 4B. 6C. 9D. 33E. 8F. 4G. 16H. 10I. 5L. 3M. 15N. 14O. 4P. 3Q. 14R. 13S. 25T. 4U. 2V. 2W. 1X. 4Y.

The meaning of this anagram was afterwards explained as follows: "The resistance of a sharp-ended ship exceeds the resistance of a current of water of the same velocity in a channel of the same length and mean girth, by a quantity proportional to the square of the greatest breadth, divided by the square of the length of the bow and stern." Rankine and his naval friends prepared an elaborate Treatise on Shipbuilding which was published in 1866.

Rankine's only brother had died while yet young, and it seems that in later life his father and mother lived with him. In 1870 his father died, and in the following year his mother. Rankine never married; when he composed the song about a bridal tour to the Carrick Hills, his eyesight had failed so that he could not read. He had undertaken to write the memoir of John Elder, a shipbuilder, and this he was able to finish in 1872. Mrs. Elder endowed his chair so that it is now called the John Elder Chair of Engineering; it was however too