54 LAWRENCE HARGRAVE. 



fast in a clamp when the tin pen has been properly adjusted to 

 the paper. The indicator piston is 11*4 millemeters diameter. 



•The performance of No. 13, the bow-screw machine, may be 

 summarized as follows : — From two of the weight-lifting chrono- 

 grams, the efficiency of the engine is determined by Mr. J. A. Pollock 

 to be *29. The flight was one hundred and twenty-eight feet 

 horizontal with a fall of three feet ten inches. The time of flight 

 was eight seconds. The speed therefore was 10*34 miles per hour. 

 The engine made forty-nine revolutions with a reduced pressure 

 of forty-five pounds per square inch. The stroke of the engine is 

 1-126 inches and the cut-off at *8. The area of each piston is *994 

 square inches. The total distance swept through by the three 



pistons is therefore x 12 x = 11 03 feet ; and the work done 



during the flight is 11*03 x -994 x 45 x -29 = 143 ft. lbs. This 

 neglects -2 of the stroke where possibly some expansion took 

 place. 



The screw is right handed, 31*6 inches diameter and one hundred 

 inches pitch. The total surface of the two blades is seventy square 

 inches. A listing moment was produced that one ounce at 32-25 

 inches to the right of the centre of gravity was insufficient to 

 counteract. The machine listed slightly and turned to port, 

 making a curved course. Two intermediate points were noted 

 over which the machine passed, so that there is a possible error 

 in the distance flown. Taking the flight to have been one 

 hundred and twenty-eight feet the slip of the screw was 69%. 



By using -29 as the efficiency of the 40-5 oz.* machine described 

 in June 1890, the work done by it as tabulated at page 256 of 

 the Proceedings of the Royal Society of N.S. Wales for that year, 

 should be eight hundred and seventy foot-pounds and that of the 

 74 oz. machine seven hundred and eighty-nine foot-pounds. The 

 foot-pounds for the cross-bow models in the same table should be 

 corrected to 3-8. And on Plate xviii., for stroke 1*27 inches read 

 2-27 inches. 



* Note — The 40-5 oz. machine is now called No. 10, and the 74 oz. one 

 is No. 12. 



