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Rh shell-fire by the aggregate weight of the projectiles thrown, it is evident that we should only be making an approximation to the truth.

If we go further and endeavour to compare the relative value of armament of diverse type for aeroplanes, as, for example, in computing the relative merits of machine-guns and small artillery in any given case, we are inevitably thrown back on examining the service for which the armament is required; it is impossible to institute a direct quantitative comparison which would be generally applicable. If it be conceded that in any particular case a given weight in the form of shell is of greater effect than the same weight in the form of bullets, then we have a prima facie case for the use of artillery. If, on the other hand, it is conceded that the bullets would do the greater mischief, then a machine-gun armament is indicated. However, although the weight of ammunition is a matter of first importance, the weight saving and convenience of the machine-gun in itself are sufficient to give it a preference where the other advantages are not overwhelmingly against it.

§51. Weight thrown per minute; Machine-Gun and One-Pounder Compared. It has in the preceding paragraph been rather assumed that the capacity of the armament, as represented by its weight-rapidity factor of fire, is a constant; this is a matter that depends, firstly, upon the mechanism of the gun. The Lewis gun, which has been taken throughout these articles as representative of the machine-gun in its aeroplane usage, will fire as an ordinary maximum 600 rounds, or 18½ lb, of lead per minute. Unfortunately, there is no standard 1 pounder with which to institute a comparison. The 37-mm. gun is given by different makers as throwing in some cases a projectile 1nblb., and by others the same bore is given as throwing 1½ lb. Also the question arises whether an