TRANSACTIONS 



OF THE 



Iftitoaajjlual Jttatttaty ufl f hto\m 



Art. I. — On a New Form of Propeller for Steam Ships. 

 By David E. Wilkie, M.D. 



[Read before the Institute, 4tli February, 1857. 



Not more than forty years have elapsed since steam power 

 was first successfully applied to the propulsion of ships by 

 means of paddle wheels, and, ever since that time, paddle 

 wheels, with a few modifications in their construction, have 

 continued to maintain their ground, notwithstanding the 

 numerous inventions that have been proposed as a substitute. 

 The most important of these inventions is the screw, which 

 was successfully brought into use in 1836 through the exer- 

 tions of Capt. Ericcson and Mr. J. P. Smith. 



With the experience of twenty years the screw has under- 

 gone several important improvements, — the most practically 

 valuable of which appears to be that of Mr. Robert Griffiths, 

 which furnishes a simple means of altering the pitch of the 

 blades, according to the velocity and the resistance. This 

 new form of screw has also the advantage of acting equally 

 well reversely, so that, in this respect, the screw and the 

 paddle wheels are very nearly equal. 



I shall not occupy your time with discussing the advan- 

 tages and disadvantages of these two methods of propulsion ; 

 but it is necessary to state, shortly, the facts that have been 



VOL. II. B 



