May 31, 1894] 



NA TURE 



105 



driven in after it, the fact being that the two conditions 

 are not opposed but simultaneous. Magnus' view was 

 further supported by the adverse criticism of the theory 

 of projectile air of the celebrated French artillerist 

 Morin, which criticism amounted to this, that when a 

 projectile was directed against a solid body it must 

 necessarily follow that so elastic a substance as air should 

 be completely reflected from the surface. I should like 

 to draw your attention to this word solid, because I 

 believe that in that we find the key to the difficulty, 

 and the apparent paradoxes presented to us are to be 

 explained by the fact that the results are wholly depen- 

 dent upon the simple question of the relative viscosities 

 of the substances entered. To solve this, I employed the 

 same falling bodies, and examined their entanglement of 

 air in water and glycerine respectively, and found that 

 whereas in the case of water, Laroque's non-floating rod 

 drove air in front of it as well as probably at the side, 

 yet when the same rod was caused to fall into glycerine 

 of high concentration there was no air in front, but air- 

 bubbles could be seen clinging to the sides of the rod. 

 Further, in glycerine the entanglement of air in the 

 funnel formed by the base of the bullet, as described by 

 Magnus, was very striking. It appeared to me that 

 whatever air was driven in front of it was wholly re- 

 flected by the sufliciently viscous fluid, and hence it must 

 be, a fortiori, still more completely reflected from the 

 surfaces of hard and soft solids like the skull and brain 

 respectively. 



To sum up, the so-called projectile air can have no 

 real bursting effect, since, as I have demonstrated, in the 

 first place it exerts very feeble pressure, as tested on a 

 delicate vane, and in the second place it is certainly 

 easily reflected from surfaces of but moderate density. 



The InfluLtice of Rotation produced by Rifling. — It is 

 commonly thought that the spin of the bullet communi- 

 cated to it by the rifling of the barrel, and which is very 

 great, causes a considerable amount of the disturbance 

 created in the interior of moist substances, which ii 

 usually spoken of as the bursting or explosive effect. 

 Kocher thought that this would not beappreciable,and that 

 the rotatory movement would only cause the disoliced 

 particles to take a course tangential to the surface of the 

 bullet rather than perpendicular. Although the smooth 

 surface of the bullet of course adds force to the idea that 

 its rotation is not very effective, it is obviously a matter 

 of both interest and importance that the matter should 

 be more closely studied. Colonel Henrad made plaster 

 casts of the tracks of shots, and obtained distinct spiral 

 markings indicative of the rotation in question. Acting 

 on this suggestion, it was easy to institute a scries of 

 experiments of the following kind. Pure modelling clay 

 of firm consistence (for the influence of the water present 

 vide infra) was rendered homogeneous by kneading, 

 shaped into square blocks of varying length, and sup- 

 ported in a hard flat surface or in a box, the ends being 

 open. The cavity made by the bullet in entering and 

 traversing the mass was then filled with liquid plaster-of- 

 paris, and a cast obtained. Examples of such casts are 

 before you, and they completely display the rotation in 

 question. 



The first point which has to be borne in mind is the 

 relation of the rotation to the projection or forward 

 movement of the bullet. In passing through a body of 

 little resistance like the air, it is clear that for every given 

 unit of distance travelled, the displacement evoked by 

 the rotation must be something very small, because 

 although the bullet turns one and a half times in travers- 

 ing the barrel, that is nearly a yard in length conse- 

 quently, so far as the rotation is concerned, that for a 

 unit, say one inch, of the flight of the bullet would be 

 extremely small, namely about one-twentieth of the cir- 

 cumference of the bullet, which, roughly speaking, would 

 be (for the '380 bullet 1 about one-twentieth of an inch, the 



NO. 1283, VOL. 50] 



insignificance of which is obvious. The matter, however, 

 assumes a somewhat different aspect when a bullet is 

 engaged in a solid substance through which it is forcing 

 its way with rapidly diminishing velocity. In such a 

 case, where the projection journey of the projectile is 

 quickly coming to an end, it becomes of special import- 

 ance to see what is becoming of the factor of rotation. 

 The plaster casts obtained in the manner indicated show 

 clearly enough the interestinir fact that the rotation 

 persists to the end, when the bullet has simply taken its 

 course through the atmosphere, and then entered the soft 

 clay. Further, the casts also show what is a necessary 

 deduction from our earlier considerations on this matter, 

 namely, that as the rotation is preserved till the end 

 of the trajectory, the twist is proportionately more 

 pronounced as the forward movement is lost. 



It is for our present purpose important to see whether 

 the rotation is well marked when the projectile is com- 

 pletely deformed. To examine this point a new series of 

 experiments were undertaken, in which the bullet was 

 first caused to penetrate a flat bone before entering the 

 clay. It is very clear that the rotation is still present. 

 In discussing this question I have left unnoticed the fact 

 that owing to the resistance of a body like clay, the co- 

 hesiveness of which of necessity varies slightly from 

 point to point, there will be a great tendency for the 

 bullet to change its direction, more especially as the base 

 is heavier than the apex, and to this change of direction 

 must be attributed in part the change of surface simu- 

 lating the rotation effects due to the rifling. The two 

 conditions, however, can be distinguished readily on 

 careful examination. 



So far as destructive effects in the brain are concerned, 

 it is therefore clear that relatively little is to be ascribed 

 to rotation. 



Projection Destructive Effects. — The destruction by the 

 bullet moving forward through a solid body is the most 

 important matter for us to consider. There are two sets- 

 of factors determining the degree of destruction in any 

 given substance. 



(i) Factors due to the bullet. 



(2) Factors due to the physical constitution of the 

 solid. 



(i) Factors due to the bullet. So far as the projectile 

 is concerned, the chief considerations are [a) its 

 momentum ; {b) its sectional area ; (c) its becoming 

 heated. 



(a) Momentum. — Although it will of course be generally 

 understood that the greater the velocity the greater the 

 damage for the same weight of shot, still, in connection 

 with the small-bore service rifles of the present day, some 

 seem to think that the small bullet, by virtue of its 

 travelling at a great pace, would pierce the tissues with- 

 out causing much general damage. The fallacy involved 

 in this belief we shall see directly ; but a single glance at 

 the casts arranged in order of the velocities of the bullets, 

 shows immediately the unreality of the notion. In every 

 case the particles of the substance are hurried forward 

 (particularly evident in the casts before mentioned) ir> 

 front of the bullet, and thus by increasing the size of the 

 moving mass such particles practically constitute a larger 

 projectile. Much destruction is due to this, as Delorme 

 has more particularly demonstrated in the well-known 

 case of firing a bullet into a book, wherein one may see 

 the laceration of the pages successively increased, 

 although the momentum of the bullet is steadily dimin- 

 ishing and in proportion to the increasing laceration, so 

 discs of increasing diameter are found in the cavity, 

 having been cut from the preceding pages. The 

 hurrying forward of the particles is very beautifully 

 shown by Prof. Boys in his photographs of the 

 debris of glass plates after a bullet has passed 

 through them. In one case a large fragment of glass is 

 shown to be moving parallel to the bullet, i.e. with the 



