TRANSACTIONS OF THE SECTIONS. 237 



tube, in the centre of which is fixed another tube \ less in diameter, and so fixed that 

 air may pass freely in the space between the two : the lower end of this inner tube 

 has a trumpet-shaped termination, which enters into the globe, reaching within two 

 inches of the top of the chimney of the Argand burner of the lamp. The upper ends 

 of the tubes terminate in a sort of lantern-top, which is divided into a lower and 

 upper compartment ; from the lower compartment the larger tube conveys the air 

 required by the lamp for effecting combustion ; while through the upper compart- 

 ment is discharged, by the inner or centre tube, the vitiated air as ejected from 

 the lamp. 



On a New Gas-burner. By the Abbe Moigno. 



On an Automatic Injector for feeding Boilers, by M. Giffard. 

 By the Abbe Moigno. 



On a ffclico-meter, an Instrument for measuring t/ie Thrust of the Screw 

 Propeller. By the Abbe Moigno. 



On an Application of the Moving Power arising from Tides to Manufac- 

 turing, Agricultural, and other purposes ; and especially to obviate the 

 Thames Nuisance. By the Abbe Moigno. 



On the Performance of Steam-vessels. By Vice-Admiral Moorsom. 



At the last Meeting of the Association, the author presented a paper in which 

 some account was given of the ' Erminia :' he now presents further particulars of 

 that vessel, with remarks on performance. 



The performance at the measured mile, being the mean of four trips, was as 

 follows : — 



Speed of vessel, knots 6 



Speed of screw, knots 6*72 



Slip per cent 10*66 



Revolutions per minute 52*37 



Indicator horse-power by eight diagrams 54*59 



Mean pressure in boiler 51*SO lbs. 



Mean pressure in cylinder 32*07 lbs. 



From calculations previously made, it was anticipated that a speed of six knots 

 would require 90 horse-power, and that the slip might be about 21 per cent. The 

 resistance of the vessel at six knots in smooth water was first estimated by resolving 

 the resisting surfaces into an equivalent plane surface, and deducing the specific 

 resistance of form by an empirical application of the method of Don Gorges Juan. 

 This gave 2763*5 lbs. It was, secondly, estimated by another empirical process, 

 which I had found to answer within given limits of form, and was founded on 

 Bcaufoy's experiments. This gave a specific resistance of 18961bs. The pitch of a 

 screw of 8 feet diameter, to produce a resultant thrust of 2763*5 lbs. at six knots, 

 is 1337. The pitch selected being 13 feet, the slip to balance should be 21*11 per 

 cent. Then how comes the actual slip to be only 10'66 per cent. ? 



The answer to this is the key to the whole operation, and it is this : — 



The direct thrust of the screw under the actual circumstances of the trial was 

 2122'7 lbs., and the resultant was 1896*4 lbs., and the difference of .the ratios of 

 their square roots is 10*66. 



But 1896 lbs. is also the specific resistance as estimated by the second method, and 

 as the thrust calculated by an independent process comes out the same, within half 

 a pound, the concurrence of the two seems to establish that as the actual resistance 

 at the time of the trial. Such concurrence may not, however, be held to be con- 

 clusive. 



