254 LAWRENCE HARGRAVE. 



^double vibrations of the engine, and the receiver pressure. The 

 first two are automatic, the last depends on the quickness of the 

 <eye and hand. It has since been made to record antomatically 

 the receiver pressure and the reduced pressure. 



A comparison of the pressure gauges with the Marine Board 

 -standard, necessitated a correction to the pressures on Plate 2, 

 Vol. xxiv. of this Society's Proceedings, they should be — 

 Test pressure ... 347 lbs. per square inch. 

 Working pressure 207 lbs. „ 



This will considerably modify the theoretical amount of work sup- 

 posed to have been done in the experiment described. Instead of 

 2500 ft. lbs. it should be 3000, an error in computation having 

 also been discovered. Practically, an equal volume of air is now 

 forced to develope 450 ft. lbs. in 25 seconds ; this is actual weight- 

 lifting. 



An enlargement of about 6 cubic inches capacity was made in 

 the air pipe of No. 4 Tin engine, this was surrounded by a jacket. 

 A piece of cotton wool soaked in methylated spirits was placed 

 in the jacket and lighted shortly before turning on the air. No 

 appreciable difference in the number of double vibrations or their 

 rapidity was produced thereby. 



Two other forms of flapping engines and another rotary one 

 were designed, but they are vastly inferior to Diagram 2, which 

 was then made. The valve gear is now forward of the cylinder, 

 but its exposed position has not led to its damage in any of the 

 six trials, and it is very accessible for adjustment. The steel 

 wing; levers are soldered to tin sleeves which form the sockets for 

 the wing arms. The wings are exactly the same area and length 

 as those of the 40*5 oz. machine, but they are made of oak with 

 five ash cross bars instead of four. 



The reducing valve, Diagram 3, is a modification of a dead 

 weight one shown to the writer by Mr. Cruikshank, and the 

 plotting of the mean of four chronograms shows its action to be 

 reliable, although in Trials 5 and 6 it was necessarily screwed up 

 so tight that its action must have been very slight. There is a 

 counter attached to the side of the receiver, it consists of a GO 

 tooth clock wheel with two ratchets, one of which is pulled up 

 and down by a string fastened to the wing arm. The interest 

 felt in the flight of the machines has always prevented any attempt 

 being made to count the flaps. The indicator diagrams are rect- 

 angular so the pipes and ports are now the right size. 



The sides of the body plane slope upwards 18°, and the paper 

 area is slightly less per pound weight than the 40 - 5 oz. machine 



