March 5, 1920] 



SCIENCE 



227 



Since the muzzle velocity is 2,300 feet per 

 second and the screens are 20 feet apart, this 

 frequency is nearly equal to that of the pre- 

 cessional motion at maximimi yaw. 



The discussion just given shows what a 

 difficult matter it is to measure the retarda- 

 tion of a projectile by firing through screens. 

 For the retardation must be not only a fimc- 

 tion of the velocity but also of the yaw. As 

 the latter is periodic there will be a periodic 

 term superimposed on the general term. 

 While the ordinary law may lead one to sup- 

 pose that the retardation would continually 

 decrease as the velocity dies down it may 

 actually go through the cycle of decrease, in- 

 crease. For the same reason we may find that 

 the retardation for a shell fired from a gun 

 rifled 1 in 25 may differ from that for the 

 Bame shell and velocity when the rifling is 

 1 in 50. 



It has been indicated that previous to the 

 introduction of the method of short arc com- 

 putation by Moulton there had been little 

 change in the field of exterior ballistics in 

 America for several years. In experimental 

 work there had been rather slow progress. 

 That the progress was slow was not so much 

 the fault of the Army as it was due to the 

 non-military policy of the coimtry. When no 

 importance is attached to military affairs by 

 the people we can not expect our army officers 

 to place their service in a position of world 

 prominence. 



Recently my attention was called to a letter 

 which may throw light upon one reason for 

 the fact that experimental work was very 

 limited. This letter was written in 1907 from 

 the Ordnance Board to the Chief of Ord- 

 nance, requesting that $40 be allowed for ex- 

 periments in determining the effect on range 

 produced by changing the points or ogives of 

 50 three-inch projectiles. The experiments 

 were authorized and the money allowed. 

 Trials with only 15 of the 50 projectiles 

 showed that the range was increased from 

 5,042 to 5,728 yards. It was reported that 

 the coefficient (jSc) had been changed from 

 .97272 to .68705. (Note again the extra- 



ordinary accuracy in measuring this quan- 

 tity!) The colonel in charge of the experi- 

 ment deemed further work unnecessary, for 

 he writes (9th indorsement) : 



Having established the probable form of the 

 field projeetUe the board reeommends that the re- 

 maining 35 experimental shells be made to con- 

 form to this design. 



However, the Office of the Chief of Ord- 

 nance considered that the last word had not 

 yet been said concerning the best form of 

 projectile, and ordered certain other varia- 

 tions to be made in 10 of the remaining 35 

 projectiles. To provide for this further test 

 it was stated that " a sum of $25 . . . has this 

 day been set aside on the books of this office 

 as a special allotment." (And this was only 

 seven years before the World War started.) 



It may be further stated that to this letter 

 authorizing $65 for experimental tests of shells 

 there were 15 indorsements. Those of you 

 who have been in the service will appreciate 

 what this must have meant in the time of 

 stenographers, messengers, filing clerks, and 

 high-salaried officers. 



That perfection in the form of projectiles 

 had not been secured was made evident by a 

 series of experiments, rather crude as judged 

 by physical standards, begun at Sandy Hook 

 in 1917, and continued at Aberdeen in 1918. 

 It had been noticed that there was very large 

 dispersion of the shells of the 6-inch gun and 

 the 8-inch howitzer. Various book theories 

 were advanced to account for these disper- 

 sions, but finally upon an examination of some 

 recovered shells and as a result of the in- 

 formation obtained by firing through card- 

 board screens, the true explanation suggested 

 itself. The rotating band on these shells had 

 a raised portion, called a lip, at the rear of 

 the band (Fig. 3). The purpose which this 

 lip was supposed to serve was to act as a 

 choking ring to prevent the escape of the 

 powder blast past the projectile and to seat 

 the projectile at a definite place in the gun. 

 It was seen in the case of the recovered 

 projectiles, and it was evident by the hole 

 formed in the cardboard screen through which 

 the projectile had passed, that these lips were 



