196 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1916. 



Then came the desire to actually see this peculiar manifestation 

 and, incidentally, to conclusively prove the silencer. It was always 

 a bit difficult to prove to the ordinary mind that the noise heard when 

 shooting a rifle equipped with a silencer was made out in the air 

 beyond the silencer and that the latter should not be held accountable. 



The United States Navy, through their Ordnance Department, 

 produced the best photographs which have been taken. These were 

 made by mounting the gun in a dark room and setting up the camera 

 with an open shutter along the line ©f bullet flight. Two wires lead- 

 ing from an electric condenser were dropped down directly beside 

 the trajectory so that the bullet would short circuit these wires when 

 it passed and create a spark, the duration of which was of radio 

 frequencj^, possibly something approximately one five hundred 

 thousandths of a second. This almost infinitely short exposure gave 

 a clear photogi'aph of the bullet and the variation in density of the 

 air in the bow wave caused a variation in the refraction of the light, 

 causing less light to fall where the pressure was high and more light 

 where the pressure was low. Beautiful pictures of the noises made 

 when the gun is discharged were obtained. Some of these are shown 

 herewith. A series were taken showing the noises when the service 

 rifle without silencer was fired and another series with the silencer. 

 In the former, the report noise is shown, the birth of the bullet flight 

 noise, and the bullet itself. In the latter the entire absence of report 

 noise is shown and the very high efficiency of the silencer dem- 

 ontrated. 



Plate 1 (photo I) represents tke condition existing immediately 

 following the emerging of the bullet at the muzzle of the Springfield 

 rifle without silencer. The two vertical wires are shown and the 

 bullet is enveloped in the mass of powder gases and can not be seen. 

 The first wave appears to be made from a rush of air out of the 

 muzzle and the main report noise wave is shown just back of it, 

 being the broad dark line, irregular in places. 



Plate 2 (photo J) represents conditions just a bit later. The bullet 

 has emerged from a cloud of powder gases and has just begun the 

 creation of its bow wave. It is shown puncturing the main report 

 noise which shows particularly strong in this picture. By looking 

 carefully the noise waves set up by flying particles of unburned 

 smokeless powder can be seen. 



Plate 3 (photo N) represents conditions still later and out beyond 

 the disturbance of the blast of gas from the muzzle. The bullet flight 

 bow wave has developed further and the greater velocity of the 

 bullet over the report noise wave is very well shown. It is not plain 

 at this time why the main report wave should be divided at the rear 

 of the bullet. This completes the series of photographs taken with- 

 out silencer. 



