THE EXHIBITION OP 1862. 
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more accurate and far-reaching weapon than the old smooth 
bore ; for without some knowledge of these, the changes can 
scarcely be appreciated. Neglecting the form of the outside 
at present, let us consider the interior only, and following the 
Irishman’s receipt for making a gun, as the first stage, “ take 
a long hollow,” and we have the long cylindrical bore, closed at 
one end, in which the charge of powder is ignited, and which, 
becoming very rapidly, though not instantaneously, converted 
into gas, drives the projectile — a spherical bullet — before it in 
one direction, and the gun in the other.* Unless the gun be a 
breech-loader, the bullet must necessarily, for ease in loading, 
be rather smaller than the bore. Through this interstice, 
termed windage, a great deal of the gas escapes uselessly; 
whence there is a great loss of initial velocity. And further, 
the bullet goes bounding along the bore, striking first against 
one side and then the other, and leaves it, not in the direction 
of the axis of the piece, but in some other direction, depend- 
ing on the side it struck last, which is one cause of inaccuracy ; 
but it also, either from having rubbed against one side of the- 
bore more than the other, or from its not being perfectly 
homogeneous, — when the centres of figure and gravity do not 
coincide, — carries with it a spinning or whirling motion, 
which is another and more important cause of inaccuracy. 
For this rotation causes great deflection, in the following 
manner: — Owing’ to its rapid motion, the air becomes more 
condensed in front of the bullet than behind ; in fact, when, 
the velocity is more than 1,344 feet per second (the rate 
at which air will rush into a vacuum), there is a complete 
vacuum behind it. If we imagine the bullet to combine with 
its motion of translation, a rotation from left to right as we look 
down upon it while facing in the direction in which it is going ; 
that is, representing’ the bullet in plan by a shilling, in the 
direction that the superscription runs ; then the air being 
denser before than behind, there will constantly be a greater 
friction on the anterior than on the posterior half of the bullet, 
— a friction that is opposing the motion of rotation of the front 
half to the right, and therefore tending to deflect or make the 
* The permanent gases generated occupy, it is computed, at the temperature 
supposed to he produced — 3,000° Fahr., — a volume of about 2,000 times the bulk 
of the powder. But this point, as well as whether, at this high temperature, 
Marriott’s law of the elasticity varying as the density holds good, has never been 
accurately determined. If, however, we take Dr. Hutton’s estimate, which 
is rather a low one, that the first force of fired gunpowder is equal to 2,000 
atmospheres (30,000 lb.) on the square inch, and that, as Robins computed, 
the velocity of expansion is about 7,000 feet per second, we have some idea 
of the force. 
