234 CAUSES OF DRIFT. 
flat-head to 8:1-inch) the area of the annular curved portion is greater 
than that of the flat portion of the front surface presented to the resis- 
tance of the air during flight. These proof cylinders should not be 
termed, as they are in the Report, flat-headed.’” 
“ Besides the mere amount of rounded surface which gives with 
right-handed twist a right deflection, the rounding off of the shoulder 
changes the action of the air on the shot, doubtless by facilitating its 
passage from the front, and this has been clearly pointed out by 
Professor Bashforth, who, quoting the results of experiments, says : 
‘The slight variation in the resistance to these latter forms lead to the 
conclusion that the amount of resistance offered by the air to the 
motion of elongated shot is little affected by the more or less pointed 
apex, but depends chiefly upon the form of the head near its junction 
with the cylindrical body of the shot.—(Bashforth’s ‘ Motion of 
Projectiles,’ p. 30). The gyroscope shows clearly the great effect of a 
pressure near the cireumferance compared to one near the centre of the 
flat head.” 
I had already said in “ Modern Artillery,”* “that, to lay down one 
rule for all cases of velocities, angles of elevation, different positions 
of centre of gravity, varying direction and strength of wind, with 
either flat-headed or pointed projectiles, is evidently impossible, and 
the writer has not attempted to do so.” 
“In the meantime, the writer is satisfied by what has already been 
done, that if a flat-headed projectile be fired with a high initial velocity, 
with its axis steady on leaving the bore, with a velocity of rotation 
sufficiently high to keep the axis steady, and at such an angle that the 
resultant of the resistance of the air will act upon the flat surface, the 
deflection with a right-handed rotation, will be to the /eft, according to 
the theory of Magnus, not Bashforth.” 
It will then I think be admitted by those capable of forming a sound 
opinion on the results of the experiments described, and the conclusions 
that have been drawn from them, that at the low angles of elevation 
and high velocities with which elongated projectiles are fired from 
ordnance and small arms, the chief cause of drift is the conical motion 
of the front of the shot due to the action of the resistance of the air to 
the forward motion of the projectile, and that the rolling effect has but 
small influence ; also that the drooping of the head of the shot is due 
to the same cause, and cannot be due in any way to the rolling 
effect. 
When, however, a projectile is fired at a high angle of elevation with 
a small charge, and consequent low velocity and long time of flight, the 
circumstances are changed. ‘The angle of descent in such cases is very 
great, while the resistance of the air to the forward motion of the shot 
becomes slight, and as it descends from a great height at a high angle, 
in certain cases nearly vertically, the density of the air becomes very 
great below the projectile, and the rolling effect, caused by the friction 
of its under surface on the condensed air resisting its descent, may 
have a very great effect on the drift, while the resistance opposed 
to the forward motion being slight, it produces little effect on the drift 
during the latter portion of the flight. 
This was probably one reason why the three proof shot fired in the 
Royal Arsenal, with a very low charge, and at 40° of elevation (as before 
* Apendix V 
