January 17, 1901] 



NATURE 



279 



" Mix equal parts of A and B, and allow the plate to 

 soak in the mixture for ten minutes or a quarter of an 

 hour, in the dark. Wash well. 



" (3) Transfer the washed plate to a solution of three 

 oz. of sodium hyposulphite in 20 oz. of water. Allow it 

 to remain for half an hour, and then wash the plate in 

 running water for three hours. 



"(4) Prepare a 'clearing' solution according to the 

 following formula : — 



Alum I ounce 



Citric acid i ounce 



Ferrous sulphate ... ... 3 ounces 



Water ... ... ... ... 20 ounces 



"Allow the plate to soak in this for ten minutes, and 

 then remove and wash in running water for six hours. 



" The sulphocyanide and gold solution has the property 

 of precipitating gold on the image, and rendering it of a 

 blacker colour and diminishing the chance of fading. I 

 should think you will find it useful always to use the clear- 

 ing solution and the sulphocyanide and gold solution in 

 your usual process." William J. S. Lockyer, 



VIBRATION OF GUN-BARRELS.^ 



THIS research on the vibration of gun-barrels is a 

 continuation of former investigations on the nature 

 of vibrations set up in a gun-barrel when fixed, with a 

 view to discover how the error of departure is affected 

 by rapid oscillations of the barrels when firmly clamped. 

 The authors' experiments were made on three small-bore 



7 y 



Fig. I.— 8 mm. Cal. gun clamped in coik support, yibration curve of a point at the muzzle, y Disengaged spark at 

 the instant at which the shot leaves the muzzle ; y' Disengaged spark at 4-5 m. distance from the muzzle. In the 

 unconstrained method of holding the weapon, the amplitude of the vibration is not so strongly marked as when it 

 is clamped. (See Fig. 2.) 



" (5) Prepare in advance two solutions, C and D. 



So'ution C. I Solution D. 



Ammonium sulpho- | Gold chloride 15 gr. 



cyanide 100 gr. Water 15 oz. 



Water 100 oz. | 



" For use take i ounce of each, and add 8 ounces of 

 water. Soak the plate in 'this mixture for ten minutes, 

 and at the end of the time remove and wash it in running 

 water for half an hour. Transfer to a dish of distilled 

 water, where it may remain for an hour. Finally, drain 

 on blotting-paper, and allow to dry. 



"The separate solutions, A, B, C and D, will keep for 

 an indefinite tim?, and the same may be said of the 



rifles, placed at their disposal by the firm of Mauser — 

 viz., one 8 mm. experimental rifle furnished with a wood 

 stock, one 7 mm. Spanish model, and one trial gun 6 mm. 

 — in all cases smokeless powder was used. In their early 

 experiments the rifles were clamped firmly when fired, 

 but in their recent work this method of support was 

 abandoned, as they found that the clamping imposed 

 restraints which altered the character of the shooting of 

 the rifles and also their mode of vibration. This is by 

 no means a new discovery. The late W. E. Metford, of 

 well-known rifle repute, showed long ajjo (1870) that the 

 shooting of a rifle was greatly changed when the barrel 

 was securely clamped to a heavy mass of iron. In order 



Fig. 2. — Gun 7 mm. Cal. Held by means of artificial marksman, and fired by pneumatic method. 



clearing solution, if kept tightly corked. But when mixed 

 together they will not keep, so fresh mixtures should be 

 made each time. 



" I have given you the full process adopted on the 

 plates you sent me, but I think some of them may be 

 omitted with no disadvantage. For example, I should 

 like to try if the soaking in hyposulphite may be dis- 

 pensed with. I think it can, but 1 only tried leaving it 

 out on the plates you sent that had not faded. 



" I always found the great secret of preventing images 

 from fading out was to wash them very well in running 

 water. The clearing solution allows the time of washing 

 to be a little shortened, but not much. 



NO. 1629, VOL. 63] 



to avoid this source of trouble the experimental guns 

 were sometimes embedded in cork and sometimes sus- 

 pended pendulum fashion by ropes, so that they were 

 practically unrestrained and the condition of support 

 approximated to the normal one, namely, the rather free 

 support of the hands and shoulder of the marks.iian. 

 The movements of the barrels were recorded by means 

 of photography on a moving sensitive plate. Two 

 methods were employed for firing the guns, viz., an 

 electro-magnetic trigger-puller, and a pneumatic method 

 in which a small piston, moving in a cylinder attached to 



1 " Untersuchung iiber die Vibration des Gewehrlaufes." Von C. Cranz 

 und K. R. Koch. Pp. 23 ; 4 plates. (Munchen, 1900.) 



