MECHANICS AXD USEFUL ARTS. 33 



and hence its name. Mr. Granthara said the propeller had been tried in 

 the Birkenhead Docks with good effect. Proc. British Association. 



CUNNINGHAM'S PLAN FOR REEFING TOPSAILS. 



This plan consists of an arrangement by which the yard-arm is made to 

 turn round as it is lowered by a pulley fixed to the mast, and the slit in 

 the centre of the sail through which the rope passes, to effect that move- 

 ment of the yard-arm, is closed by a sail-cloth valve that preserves the 

 action of the sail intact. 



APPLICATION OF THE SCREW-PROPELLER TO SHIPS OF WAR. 



The following extract from a report to the Secretary of the Navy, by 

 Lieutenant Walker, on the applicability of the screw-propeller to existing 

 ships, will be found interesting : 



One of the most interesting and important subjects to which I directed 

 my attention while abroad, was the results of the trials that have been 

 made in France to test the applicablity of the screw-propeller to ships of 

 war of the largest class. Many of these results have not yet been publicly 

 made known, and I found many obstacles in the way of a thorough inves- 

 tigation of the subject. The officials to whom I applied for information, 

 with a great deal of outward politeness and apparent readiness to oblige, 

 were evidently indisposed to afford an officer of a foreign service all the 

 desirable means of becoming acquainted with improvements from which 

 they hoped to reap advantages. I succeeded, however, in obtaining some 

 reliable information upon this important subject, and now subjoin the 

 results of my investigations ; but I think it necessary to remark that more 

 extensive personal examination and observation, both in France and Eng- 

 land, than I was permitted to make, is necessary, in order to enable the 

 department to judge of the eventual success of the experiments in both 

 countries. 



The French have afloat eight ships-of-the-line, five of which have 

 already been fitted with propellers, and the remaining three are now 

 receiving their machinery. Of these, the Charlemagne, the Napoleon, 

 and the Montebello have been at sea, and have performed so well that the 

 most sanguine hopes are entertained that the adaptation of the screw to 

 ships-of-the-line will vastly increase the effective force of their navy. 



The Napoleon is the only one of these ships constructed especially for a 

 propeller. Her dimensions are as follows ; 



