THE EOYAL ARTILLERY INSTITUTION. 
167 
Recently a chronographe electro-balistique has been invented by M. P. 
le Boulenge, Lieutenant d'Artillerie, which has been tried and compared 
with Major Navez’s electro-balistic pendulum, by M. Melsens, Membre de 
FAcademie Royale de Belgique. He states that M. Boulenge, in his 
memoir, renders what is just to Major Navez, remarking, “Cet officier en 
effet a donne, le premier, a FArtillerie un appareil remplissant toutes les 
conditions exigees pour etre utilement employe aux recherches balistiques; 
on sait que les essais faits en Angleterre, en France, en Allemagne par des 
savants illustres, par des militaires distingues, aides d'ingenieurs et de 
fabricants habiles, avaient laisse sans solution pratique la question de la 
determination des vitesses des projectiles pour tous les cas possibles, tant 
pour les armes portatives que pour les armes de fort calibre, tirant sous 
des angles variables.” 1 Experiments were made with various powders 
to compare the two. Belgian instruments. The velocity of the same 
projectile was measured by both instruments for a point 35 metres from the 
gun. The following list gives the mean velocities in m.s. of five or six 
rounds for each kind of powder as measured by the two instruments : 3 — 
Navez . 373*9 
376*1 
369*6 
371*0 
367*1 
375*1 
368*7 
Boulenge... 367*9 
366*6 
368*2 
366*8 
361*4 
369*7 
364*9 
Difference... —6*0 
-9*5 
-1*4 
-4*2 
-6*7 
-5*4 
-3*8 
Navez . 359*1 
352*7 
369*7 
368*2 
366*7 
351*4 
Boulenge... 355*9 
346*0 
365*2 
3648 
366*7 
353*4 
Difference... —3*2 
-6*7 
—4*5 
-3*4 
0*0 
+ 2*0 
Or, converting the differences of the means of the velocities, as determined 
by the two instruments, into feet-seconds, we find them: —19*7, — 31*2, 
-4*6,-13*8,-18-7,—17*7,-12*5,-10-5,-22*0,-14*8,-11*2, Q;0 and 
+ 6*6. M. Melsens appears to give the preference to M. Boulenge's instru* 
ment, but lie makes the remark, “Des experiences novelles et nombreuses 
diront ou est la verite absolue.” 3 * Now it is really remarkable that two 
instruments with any pretensions to accuracy should give such contradictory 
results. Five or six shot are fired, the velocity in each case is measured by 
two instruments. The mean of the velocities given by one instrument is 
compared with the mean of the velocities given by the other, and they diffeT 
in one case 31*2 f.s., in another 22*0 f.s., in another 19*7 f.s., and so om 
The difference of the means varies from — 31*2 f.s. to + 6*6 f.s. Thus so long 
as instruments are used without check, there will always be uncertainties to 
be settled by new and more numerous experiments. It is the great fault of 
these instruments that, whilst they are something near the truth, they are not 
sufficiently exact to give the law of the resistance of the air. But this is the 
problem that must be solved by any instrument that pretends to accuracy. 
This must be regarded as the test of the value of any chronograph. Robins 
was not content merely to determine a list of initial velocities, for he at once 
proceeded to deduce the resistance of the air to projectiles moving with any 
1 Melsens, Rapport sur un Chron., 1864 p. 5. 2 Ibid. Rapport, p. 21. 
3 Melsens, p. 24. 
