April I, 1884] 



NATURE 



527 



on the use of the table of the values of the thermic term 

 — before-mentioned— and a supplementary note on devices 

 to eliminate the influence of wind-pressure. 



It may be stated that of the seven plates referred to as 

 illustrating this -work, six are wanting in the copy now 

 under notice. 



ON A METHOD OF ESTIMATING THE 

 STEADINESS OF ELONGATED SHOT 

 WHEN FIRED FROM LARGE GUNS 

 T N October last it was stated in the newspapers that 

 ■'■ " at the request of Lord Alcester," and in the 

 presence of the Lords of the Admiralty, "comparative 

 trials of a Krupp gun and a 6-inch breechloader took 

 \i\z.ct greatly to tlie advmitage of the former." . . . "The 

 projectile used in the English weapon was 100 lb. with a 

 341b. charge, and that in the Krupp gun 64 lb. with a 

 141b. charge, the results from the latter being far in 

 adx'anee of the former^ If this statement be e.\act, the 

 matter calls for the most careful consideration. In such 

 a case the superiority of the Krupp gun must have arisen 

 either from the higher initial velocity, or from the greater 

 steadiness imparted to the shot by the Krupp gun, or 

 probably from both these causes combined. The com- 

 parative merits of these or any other guns could be very 

 readily settled by well-known methods ol experimenting, 

 at the expense of little more than the cost of 5 to 10 

 rounds of ammunition for each gun. There is no neces- 

 sity for a repetition of the Armstrong and Whitworth 

 competition, said to have cost some 30,000/. 



Numerous experiments were made in this country in 

 1867-6S with guns of 3, 5, 7, and 9 inches calibre, to 

 determine the resistance of the air to the motion of both 

 round and elongated projectiles. Coefficients of resist- 

 ance were then determined for all velocities between 900 

 f.s. and 1700 fs. Additional experiments were made in 

 1878-79 with elongated projectiles alone, which gave the 

 coefficient of resistance K corresponding to all velocities 

 between 43ofs. and 225of.s. But after this report had 

 been printed, which contained general tables for both 

 time and space within the above-named limits of velocity, 

 it was decided to have additional experiments made with 

 both lower and higher velocities. The final report of 

 these experiments was published in 1880, which con- 

 tained general tables for space and time for velocities 

 between 100 f.s. and 2900 f.s. The values of Kr corre- 

 sponding to the velocity v, as given in this report, will be 

 hereafter referred to as the "tabular" values of K-. The 

 weight of a cubic foot of air was taken to be 534'22 

 grains. 



In testing any new gun I would proceed, as in the 

 above-named experiments, to measure the times occupied 

 by the shot in passing over a succession of equal distances. 

 These observations would readily give the velocity v of 

 the shot at any point of its path, and also the correspond- 

 ing coefficient of resistance K;.. Then according as the 

 mean value of K;, derived from 5 to 10 rounds, was found 

 to \ie. greater or less than the taljular value of Kr, it would 

 be evident that the gun on its trial gave a less or greater 

 degree of steadiness than the average of the guns used in 

 the experiments of 1867, &c. 



Let us examine the relative value of these four guns in 

 rounds where the middle velocity was about 1280 f.s. 



Rounds 6-12, 124 and 126 were fired from the 3-inch 

 gun, with projectiles of 9 lb., giving for K,.,s(, respectively 

 the values I36'5, 1107, — , ii4'5, ii8'2," 1210, ii9'2, 

 1117, and Ilf2 ; the mean of which, 1179, is 89 higher 

 than log'o, the tabular value of K,;^,,. Consequently this 

 gun falls belo~M the average in steadiness very decidedly. 



Rounds 164-168 were fired from a 5-inch gun with pro- 

 jectiles of 47'68 lb., giving for K,.,,„ respectively the values 

 1107, 98-9, 9ro, 101-5, a-nd 97'9; the meanof which, 99-9, 

 is therefore 9T below 109 'o, the tabular value of Kiog„. 



Consequently these solid 5-inch shot had a very high 

 degree of steadiness. 



Rounds 148-153 were fired from the same 5-inch gun, 

 but with hollow projectiles of 23'84 lb., giving for K,»go 

 respectively the values io5'i, ii3'4, ior5, 105-4, 107-7, 

 and 1020 ; the mean of which, 105-9, 's 3'i below 1090, 

 the tabular value of Kuao- The steadiness of these shot 

 was above the average, but inferior to that of the solid 

 5-inch shot. 



Rounds 97-101 were fired from a 7-inch gun, with pro- 

 jectiles of 123-125 lb., giving for Kuoo respectively the 

 values 109-8, 118-7, io8-6, 117 6, and 117-5; the mean 

 of which, 114-4, is 5'8 greater than 108-6, the tabular 

 value of K1300. The 7-inch projectiles were therefore 

 deficient in steadiness. 



Rounds 218-221 and 228 were fired from a 9-inch gun 

 with projectiles of 2501b. giving for K,o8„ respectively the 

 values 110-4, 104-8, 126-0, 118-9, and '3' -; the mean of 

 which, ii8-2, is 9-2 above the tabulated value 109-0 of 

 Ki;s„. The 9-inch shot were therefore very unsteady. 



We thus arrive at the character of each of the experi- 

 mental guns from the error in K,,. In the 3-inch gun the 

 error was -f 89 ; in the 5-inch gun (solid shot), — 9-1 ; in 

 the 5-inch gun (hollow shot), — 3-1 ; in the 7-inch gun, 

 -f- 5-3 ; and in the 9 inch gun, -\- 9-2. 



Some experiments were made with projectiles provided 

 with various forms of heads in 1866. Although the pro- 

 gramme was never fully carried out, the rounds fired with 

 hollow ogival-headed shot of one and two diameters were 

 tolerably numerous. The two forms of shot were fired 

 alternately, and gave the following values of Kno„. 



-f o-i 

 -t-4'6 

 •f i-i 

 -05 



-3-2 

 -f 1-6 

 -0-4 

 -o-i 

 -I- i-i 

 -4-1 

 16-8 



Means ... loS'S 



15 

 •7 

 19 

 21 



23 

 25 

 27 

 29 

 31 

 33 



Means 



The tabular value of Kuoo is 104-7, which was de- 

 rived from experiments made with ogival-headed shot 

 struck with a radius of one diameter and a half The 

 unit of K in the above cases corresponds to about the 

 1/50,000 of a second. 



M. Krupp has recently circulated some tables which 

 are based on coefficients, a little less than the tabular 

 numbers above referred to, and about such as would 

 have been obtained if I had used those coefficients only 

 which were given by the most steady moving projectiles. 

 Since 1S68 there have been great improvements made in 

 the manufacture of slow-burning powder, &c., which may 

 have tended to give increased steadiness to the shot, and 

 thus to reduce the resistance of the air slightly. Still I 

 do not think it desirable at present to reduce my co- 

 efficients sensibly, because in all my experiments the 

 velocities have been determined during the motion of the 

 shot just after it had left the gun. But when the range 

 of the shot is considerable, the direction of the axis of 

 the shot must become inclined to the direction of the 

 motion of the shot, and this must increase the resistance 

 of the air. If it was thought desirable to reduce the co- 

 efficients of resistance throughout any range in a particu- 

 lar case by ^Tjth or I'jth, &c., this could easily be effected 

 by multiplying d-^a by (I - v,y, (i - tV), &c. For 

 heavy shot the range should be extended much beyond 

 500 yards 



The pamphlet alluded to above is entitled " Table de 

 Krupp pour le calcul des vitesses restantes horizontalcs et 

 des durdes de trajet des projectiles oblongs. Essen,- 



