PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 407 



ness, then lay out the face of the muzzle with eight radial lines, equal 

 distances apart, and, beginning upon one, drill a hole parallel with the 

 bore, half an inch in diameter, coming out at the breech and leaving half 

 an inch of metal between the bore and the hole thus drilled ; then drill 

 another hole on the next radial line through lengthwise, one inch from the 

 bore, and so on, each hole being half an inch further from the bore, until 

 the outer one is four inches from the bore. Fit bronze rods into these holes 

 and fasten them at the breech with screws, so that they can have no motion 

 endwise at that end, then file off the ends of the rods flush with the muzzle, 

 when the gun and the rods are at the same starting point of temperature, say 

 sixty degrees, and we shall have a thermometer that will give nearly a cor- 

 rect indication of the quantity of heat communicated to the gun from a 

 calculation based upon the difference of expansion of the metal of the gun 

 and the bronze rods, and a positively correct indication of the place of 

 highest temperature, and consequently greatest expansion, with any num- 

 ber of discharges. To retain a record of the place and quantity of heat at 

 any of the successive discharges, make a number of molds, and fill them 

 with a composition of wax and powdered charcoal with which to take an 

 impression of the face of the muzzle. These molds should be numbered 

 and recorded at each successive discharge. Charges should be made with 

 heavy and light projectiles, and with no projectiles at all, and at long and 

 short intervals between the discharges. 



The deductions drawn from these experiments would give us positive 

 knowledge on this part of the subject, and relieve it of the mystery so 

 often referred to bj^ ordnance inspectors; while without the knowledge 

 thus attained, officers of our army and navy seem to be without justifica- 

 tion, should they place large guns in our expensive iron-clad ships and for- 

 tifications, made without consideration of the important cause of failure 

 herein presented. 



L^ When a long rifled cannon is 



fired at a high elevation, the 



([t^i^:j^^^:^^^s-**-'''"'°~ gun recoils backward on a 



plane, represented by the deck 

 of a ship, different from the 

 plane of the bore. All bodies 

 in motion resist a change of 

 direction, in the proportion of l-90th of their whole momentum, or living 

 force, for a change of direction of 1°. If one billiard ball on a table is 

 projected against another at rest, striking it at right angles 90", the one in 

 motion comes to a state of rest, giving its whole momentum off, to the one, 

 before at rest. If the one at rest should be struck at an angle of 45", the 

 ball in motion would have its direction changed 45" and it would give one- 

 half its momentum to the other. Each would roll the same distance on 

 tlie table. So, also, if the angle with which they came in contact was one 

 degree, l-90th of the momentum would be given to the ball at rest. The 

 whole sum of the momentum of a shot projected from a rifled cannon is 

 very great. At the muzzle of the gun, the resistance to a change of direc- 

 tion is sufficient to overcome the preponderance of the gun. If the bore 

 was crooked, the shot would not be much diverted, but the gun would be 



