RIFLE GUNS. 



powder, fometimes the ball was deflefted to the right, fome- 

 times to the left ; fometimes above, and at others below, 

 the true line of direftion. It has alfo been obferved, that 

 the degree of defleftion increafes in a much greater propor- 

 tion than the diftance of the object fired at : thus, at double 

 the diftance, the defleftion of the ball from the line in which 

 the piece is pointed is confiderably more than double, and 

 at treble the diftance more than treble, what it was at firft. 

 Mr. Robins fecured a rhufket barrel upon a block of wood, 

 and firing it with a ball at a board of a foot fquare, at 60 

 yards diftance, found that it miffed the board only once in 

 16 fucceflive difcharges ; yet when fired with a fmaller 

 charge, at the diftance of 760 yards, the ball was thrown 

 fometimes 100 yards to the right or left of the line in which 

 it was pointed. The direction upwards and downwards 

 was alfo found equally uncertain ; the ball, in fome dif- 

 charges, having (truck the ground zco yards nearer the 

 piece than it did at others. 



It is not difficult to account for thefe irregularities : they 

 doubtlefs proceed from the impofiibility of fitting a ball fo 

 accurately to any plain piece, but that it will rub more 

 againft one fide of the barrel thai/ another, in its paffage 

 through it. Whatever fide, therefore, of the muzzl; the 

 ball is laft in contaft with, on quitting the piece, it will ac- 

 quire a whirling motion towards that fide, iad will be found 

 to bend the line of its flight in the fame direction, whether 

 it be upwards or downwards, to the right or left ; or ob- 

 liquely, partaking in fome degree of both ; and after quit- 

 ting the barrel, this defleftion, which, though in the firft 

 inftance it is but trifling and inconfiderable, is ftill farther 

 increafed by the refiftance of the air ; this being greateft on 

 that fide where the whirling motion confpires with the pro- 

 greffive one, and leaft on that fide where it is oppofed to it. 

 Thus, if the ball, in its paffage out, rubs againft the left 

 fide of the barrel, it will whirl towards that fide ; and as the 

 right fide of the ball will, therefore, turn up againft the 

 air during its flight, the refiftance of the air will become 

 greateft on the right fide, and the ball be forced away to 

 the left, which was the direction it whirled in. If the axis, 

 about which the rotatory motion of the ball is made, pre- 

 ferved its pofition during the whole flight, the defleftion 

 would be in the fame direction from one end of the track to 

 the other ; though it is obvious, that the quantity of this 

 defleftion would ftill not be proportional to the diftance : 

 for if all refiftance of the ball were to ceafe at any part of 

 its flight, ftill the ball would neceffarily purfue the line in 

 which it then moved, and the defleftion be double at a double 

 diftance, treble at a treble diftance, and fo on. But as this 

 refiftance does not ceafe, but continue to aft upon the ball 

 throughout its whole flight, (though lefs in the latter part 

 of it than at the commencement, in confequence of the de- 

 creafe of velocity,) it is obvious that the defleftion of the 

 ball will be accelerated at every inftant, and confequently 

 increafe in a greater proportion than the diftance ; as we 

 have feen it has been found to do, from the experiments 

 above alluded to. It happens, however, from various ac- 

 cidental circumitances, that the axis of the ball's rotation 

 frequently changes its pofition feveral times during the 

 flight ; fo that the ball, inftead of bending its courle uni- 

 formly in the fame direftion, often defenbes a track va- 

 rioufly contorted. So great, however, is the tendency of 

 the ball to defleft itfelf againft the fide it rubs againft, that 

 it has been faid, though we never faw the experiments au- 

 thenticated, that a ball, when fired out of a barrel bent to- 

 wards the left hand, (and which will, therefore, be thrown 

 from the piece in the direftion of the bend,) yet as the ball, 

 in this cafe, will be forced to rub againft the right fide of 



the muzzle, and thus turn its left fide up againft the air, fo 

 it will be found to alter its courfe during the flight, and 

 bend towards the right hand, fo as to fall a confiderable 

 way to the right hand of the line in which the piece was 

 pointed. 



It will readily appear, therefore, from what has been 

 ftated, that thefe variations will be more frequent and con- 

 fiderable when the ball runs very loofe in the piece ; or 

 when, from any roughnefs on its furface, or on the middle 

 of the barrel, a confiderable degree of friftion takes place 

 between them. With a view to prevent friftion, it has 

 been propofed to greafe the ball ; but this we fhould ima- 

 gine would be of very little fervice. All that can be done 

 in a plain barrel is to have the balls call very folid and 

 true, and afterwards milled in the tame manner as is now 

 praftifed upon (hot : the barrel alio fhould be very fmooth 

 on the infide, and the ball fit it very accurately, fo as to 

 leave fcarcely any windage : yet, with all thefe precautions, 

 it is very difficult, we may fay impoffible, to prevent it 

 entirely; for gravity will conftantly aft, and friction 

 the under fide will naturally be occafioned by' the weight 

 of the ball. In faft, when we confider the caufes of the 

 aberration in the flight of balls, it will be pretty evident 

 that the only means of correfting it is by preventing the 

 ball from rubbing more againft one fide of the barrel than 

 another in paffing through it ; and by giving to the bullet 

 a motion which will counteract every accidental one, and 

 preferve its direftion, by making the refiftance of the air 

 upon the fore part continue the fame during its whole 

 flight ; that is, by giving it a rotatory motion perpen- 

 dicular to the line of direftion. The contrivance for this 

 purpofe is called rifling, and confifts of forming upon the 

 infide of the barrels a number of threads and furrows, 

 either in a ftraight or fpiral direftion, into which the ball 

 is moulded, whereby any rolling motion along the fides of 

 the barrel is effectually prevented. 



The numbers of thefe threads in a gun are different, ac- 

 cording to the fancy of the workman and the fize of the 

 barrel ; and, in like manner, the depth to which thefe chan- 

 nels or rifles are cut down, is not regulated by any inva- 

 riable rule ; but differs according to the country where the 

 work is performed, or the caprice of the artificer. There 

 are alfo different methods of charging pieces of this kind, 

 but the ufual one is as follows : after tiie powder is put in, 

 a leaden bullet, fomewhat larger than the bore of the gun, is 

 taken, and having greafed it well, it is laid on the mouth 

 of the piece, and rammed down with an iron rammer, hollow 

 at the end ; the foftnefs of the lead giving way to the 

 violence with which the bullet is impelled, that zone of the 

 bullet which is contiguous to the piece, varies its circular 

 form, and acquires the (hape of the infide of the barrel, fo 

 that it becomes the part of a male fcjrew, exactly fitting the 

 indents of the rifle. And hence it happens that, when the 

 piece is fired, the indented zone of the bullet follows the 

 fweep of the rifles, and thereby, befides its progreifive mo- 

 tion, acquires a circular one round the axis of the barrel, 

 which motion will be continued to the bullet after its fepa- 

 ration from the piece ; by which means a bullet difcharged 

 from a rifled barrel is conftantly made to whirl round an 

 axis, which is coincident with the line of its flight. And 

 hence it follows, that the refiftance on the foremoft furface 

 of the bullet is equally diftributed round the pole of its 

 circular motion, and afts with an equal effort on every fide 

 of the lir.e of direftion, fo that this refiftance can produce 

 no deviation from that line : and if, by the cafual irregu- 

 larity of the foremoft furface of the bullet, or by any other 

 accident, the refiftance fhould be ftronger on one fide of 

 1 the 



