472 
THE DRIFT OF SERVICE PROJECTILES. 
the range-table. In this case you find that the lateral acceleration goes up where 
the curvature goes up, but when the curvature falls in the descending branch, 
after what Captain Sliortt calls the critical point, the lateral acceleration becomes 
negative and largely negative, and remains so up to the end of the trajectory. I 
do not profess to understand it, but that is so. 
I hope nobody will get up and say that I have been pinning any faith to the 
range-table for things for which the range-table was not intended". Everybody 
knows that the range-tables are made for practical use and not for making mathe¬ 
matical deductions from, but still they are the only things that we have to ox) 
upon unless special experiments can be made on specially calm days, when the 
weather is made to order; and I do not know how we are to get any other data • 
and although the range-tables are not true to the last place of decimals given, 
still they are generally true and any deductions that are drawn from them must 
equally be generally true. I have purposely omitted putting any scale to these 
curves as that would imply that they were numerically exact, which I do not 
profess, but only that they show the general track of the flight of the shell. 
Captain H. B. Strange —Professor Smith stated that he thought photography 
would be a good means of ascertaining the position of the shot at different points 
on the trajectory. I believe, sir, that the Ordnance Committee have taken some 
photographs of howitzer projectiles in flight and it might be well for anybody who 
wishes to see them to look them up at the Ordnance Committee Office. Then 
though I cannot give you any further details about these photographs, what we 
have seen at Shoeburyness is the projectile suddenly arrested in fligiit, and what 
was very noticeable was the very great inclination at which the projectile strikes 
the plate—so much so that being manufacturers we had to make complaints that 
our shot were not given a fair trial. It has been stated in the paper that it would 
be necessary to have an angle of 10° inclination before it would be visible. I 
should think that the angle of inclination in striking the plates was quite 10°, 
which would be sufficient to show clearly on a photograph, these were with 4" 
quick-firing guns also 6 and 3 prs. It seems clear that there certainly was precession 
of the point of the projectile round the trajectory; to obtain the precise range at 
which the point of the projectile was in the trajectory we had to brino- the 
plates gradually nearer the guns and we found then that the point of the pro¬ 
jectile was in the centre at a certain definite distance from the muzzle for each 
nature of gun; it seemed to be down first of all, then it went up, then came 
round to the right, as has been described by the lecturer. I think that the 
fact that it does go round is proved by what I have just described. This motion, 
of course, was not owing to the air, pressure or curve of trajectory, it was really 
owing to the way the projectile started from the gun, being unsteady at start¬ 
ing ; the current of air would increase this unsteadiness; the range of the 
armour plates varied, I believe, from 50 yards to 300 yards. 
Major P. A. MacMaiion —I should like to make a remark about whut 
Captain Mansell said just now. A straight line path in the sense in which I used 
the term and in the sense in which, I believe, Captain Shortt used it, can be 
perfectly realised by firing a gun either vertically upwards or vertically down¬ 
wards ; it is not necessary to fire into a vacuum, or to suppose that the force of 
gravity is annihilated. 
Captain J. H. Mansell— I should like to ask Major MacMahon whether 
when a shot is fired vertically it would precess P 
Major P. A. MacMaiion —Yes ; I think so. 
Captain E. S. Cooper— I had hoped, sir, to have some experiments to lay 
before the gentlemen here. My line is not theory, but practice and experiment, 
and I think that on a question like this one must fit one’s theories to the practice, 
to what actually takes place. 1 managed to get hold of General Owen’s appa- 
