1904.] 



Corrections to Naval Range-tables. 



395 



It need hardly be said that the agreement is sufficient for all 

 practical purposes. 



An additional fact, of considerable practical importance, is that tljere 

 is a very simple approximation to the true correction for elevation due 

 to air-density, obtained by taking it as being a constant multiplied by 

 the product of elevation and range, and percentage variation from 

 the normal air-density. The constant varies with the type of 

 gun and with full, or half, charge; but remains the same for 

 all ranges. Thus with the 6-inch gun, Mark VII, the correction 

 range x elevation 



at fall charge is 

 range x elevation 



and at half charge it is 

 1,000,000 



Curiously enough the same formula, with a 



1,250,000 



different constant, gives the correction, at all ranges, to the elevation, 

 due to rate of change of distance during the time of flight of the shot. 



These empirical laws, combined with the muzzle velocity law 

 already mentioned, have led to the design of a most simple arrangement 

 of gun-sights corrected for the individual error of the gun due to 

 wear, and for the error of the day due to temperatures of cordite and 

 of the air, and to barometric pressure, which can be worked by the act 

 of using the range-finder, and automatically corrects for time of flight 

 with changing range. 



