At about this same time, or in 1835, the attention of Mr. F.P. Smith seems to have been drawn to the subject of the screw-propeller, and we find him taking out a patent for his form, consisting of an elongated helix or spiral of several turns, under date of May 31, 1836. Ericsson's patent followed some six weeks later, or on July 13, 1836. While it thus appears that Ericsson had been studying the problem since 1833 or earlier, according to his own statements, there is no evidence that Smith's attention was drawn to the matter earlier than 1835. Delay on Ericsson's part in the matter of patent gives the earlier date to Smith. The mere date of a patent, however, is of small moment for our present purposes. It must be admitted that the modern form of screw-propeller is quite unlike either of these original forms, although they all involve of course the same fundamental principles. Ericsson's propeller may properly be called an engineering success, built on sound principles, but improved and largely modified by the results of later experience and research. Smith's propeller, while capable of propelling a boat, was the design of an amateur rather than of an engineer, and in comparison with Ericsson's seemed to show a somewhat less accurate appreciation of the underlying principles upon which the propeller operates. In the present case, as we have noted above, the question is not so much one of invention as of influence in introduction, adaptation, and improvement. The screw-propeller was already known, but had not been introduced into and made a part of actual engineering practice. Services in this direction are all that can be claimed for any of those concerned with the question during the third decade of the Nineteenth Century. From this point of view we must give to Ericsson large credit. He had the courage of his convictions, and did not allow his work in this direction to lapse for lack of effort on his part to secure its introduction into the practice of the day.