242 CAUSES OF DRIFT. 
a straight line. This shows that the law holds in the 8-in. Howitzer 
when the velocity is sufficient to the end of the range to render any 
cause of drift, except the gyroscopic, inoperative. 
Taking the Range table the lecturer has given us, and plotting the 
first two points on a logarithmic chart, if we join these points and 
produce the line we have our curve of expectation. If the rolling effect 
is to the right the actual points found by practice should lie to the 
right of this curve. On the contrary I find every other point lies to the 
left. What does this mean? It means (see rough chart) that at the 
fe fal 
OF 
' TIME 
A . DRIET E B 
time of flight (B D secs.) instead of having a drift to the right of (A B 
yards) we have only (A Hi yards), which is less than what we would 
expect from gyroscopic considerations by (C D yards). The curve of 
expectation from the first two rounds in the lecturer’s Range table 
shows a right drift at 2,5C0 yards of 135 yards, whereas the Range table 
only gives 85 yards, or a slip to the left of 40 per cent. And even this 
is under the mark as the true curve lies somewhat below, as shewn in 
dotted lines. 
It seems to me therefore that projectiles must slip to the left in the 
descending branch and that the evidence is for that. I should like the 
point cleared up by someone who knows more about it than I do; there 
are many eminent men here to-night and I rather regret that I have 
joined in the discussion at all ; but anyhow I hope one of the theories 
will die to-night, either rolling to the right or slip to the left. 
PROFESSOR A. G. GREENHILL, F.R.S.—Sir, I hope I may be permitted to 
express my opinion that General Owen has performed a very valuable ser- 
vice to the science of artillery by bringing forward this baffling question of 
drift, which has lately been allowed to slumber. His own treatise on 
“Modern Artillery,” and the paper we have before us contain very 
valuable references to the writings of continental artillerists on the 
question ; and I have recently had occasion to go through these 
memoirs ; but although they bristle with long mathematical formulas 
I have come to the same conclusion as Major MacMahon, that they leave 
us very much where we were before. I say this in spite of the opinion 
of a distinguished authority, a French officer, Colonel Astier, who, 
writing in 1873, about the same time as General Owen was writing his 
treatise on Artillery, says in his “ Hssai sur le mouvement des projectiles 
