1892.] Energy absorbed by Friction in the Bores of Guns. 409 



taper. A feeble line in the yellow was coincident, under the condi- 

 tions employed, with the sodium line at D. 



The hydrogen line at G was distinctly seen, as well as a band or 

 group of lines between G and F. 



Nearly all the lines appear to be approximately, if not actually, 

 coincident with the lines seen in the various types of Cygnus stars, 

 the chief difference being the apparent existence of carbon, hydro- 

 carbon, and calcium in the nova. 



The colour was estimated by Mr. Fowler as reddish-yellow, and by 

 Mr. Baxandall as rather purplish. My own impression was that the 

 star was reddish, with a purple tinge. This was in the 10-inch 

 achromatic. In the 3-foot reflector it was certainly less red than 

 many stars of Group II. No nebulosity was observed either in the 

 3-foot or the 10-inch refractor, nor does any appear in a photograph of 

 the region taken by a 3^-inch Dallmeyer lens with three hours' ex- 

 posure. It should be stated that the camera was carried by the 

 photographic telescope, the clock of which had had its normal rate 

 purposely changed to give breadth to the spectrum. 



The photographs were taken and reduced by Messrs. Fowler and 

 Baxandall. The eye observations and comparisons were made by 

 Mr. Fowler alone. 



II. " Note on the Energy Absorbed by Friction in the Bores of. 

 Rifled Guns." By Captain NOBLE, C.B., F.R.S., &c. (late 

 Royal Artillery). Received December 31, 1891. 



The object of the experiments which I proceed to describe was to 

 ascertain approximately, and under varied conditions, the loss of 

 energy due to the friction of the driving ring of the projectile in the 

 bores of rifled guns. 



The rotation of modern breech-loading projectiles is generally given 

 by means of a copper ring or band on the projectile, on a plan 

 originally proposed by Mr. Yavasseur, the diameter of this ring being 

 not only somewhat larger than that of the bore, but even larger than 

 the diameter of the circle representing the bottom of the grooves, 

 and the projections which give the rotation are formed by the pressure 

 of the powder gases forcing the driving ring into the grooves of the 

 gun. At the commencement of motion the driving ring is conse- 

 quently exactly moulded to the section of the bore at the seat of the 

 shot, and under the conditions due to the pressure to which the gun 

 is at the moment subjected. 



It will readily be conceived that a band or ring, moulded as de- 

 scribed, may give rise to considerable friction in its passage through 

 the bore, and the amount of this friction may be modified to a 

 considerable extent by various circumstances. j .-. 



2 F 2 



