34 
SHORT NOTES ON PROFESSIONAL SUBJECTS. 
wagons, horses, &c., made in proportion to the real she (except of course vertically), 
according to the most convenient scales which are engraved on the inside of the lid 
of each box. Thus the scale on which a box of light field battery models is con¬ 
structed, is of course very much larger than that appropriated to the illustration of 
movements of a brigade of the three arms combined. The boxes of all kinds are 
18 x 2 inches, and as shallow as possible, so that the lids serve,—besides purposes 
of mensuration applied to the table on which the models are placed and to them¬ 
selves in column or line, &c.,—to wheel up or back, or dress lines or columns, 
which they will be found to do on a moderately smooth table, with great facility and 
correctness. 
The models for the illustration of drills appertaining to any one of the three 
branches of the army, being on a large scale, can be applied to that purpose alone, 
while on the other hand, it is submitted that the brigade models, constructed on a 
scale of one inch to 20 yards, may fairly aspire to the solution of stragetical or 
tactical problems, and enable two operators provided with boxes at either end of a 
large table, to carry out a series of manoeuvres, as outflanking, deploying, &c. 
against each other, and it is also hoped that they will serve for the illustration of 
particular campaigns, better and more correctly than military maps. 
A detailed printed description accompanies each box. 
34. Resistance of the air to the motion of projectiles. Some 
interesting experiments have lately been carried out on the resistance of the air by 
Capt. W. H. Noble, R.A., under the direction of the O.S. Committee, using the 
12-pr. B.L. rifled gun and 9-inch M.L. rifled gun, advantage being taken of 
other trials to observe a second velocity with each round. 
The trials were made with two of Navez-Leur’s electro-ballistic machines, which 
had previously been found to work so closely together, that the probable error was 
reduced to less than one foot. 
The results appear to shew that:— 
(1) The resistance of the air is practically proportional to the square of the 
diameter of the projectile. 
(2) Within the limits of 1500 and 1100 feet, the resistance appears to vary nearly 
as the velocity cubed, and employing M. Helie’s formula, given in p. 26,* 
V 
V r= - 
1+cFx’ C 
(3) When the velocity of the projectile passes below 1100 feet, there appears to 
be a gradual, but at the same time, rapid reduction in the amount of resistances 
as if the projectile were being rapidly relieved from some extra pressure, this rapid 
diminution ceases when the projectile reaches about 1000 feet, and 
(4) Within the limits of 1000 and 600 feet, the resistance appears to vary 
nearly as the cube of the velocity, and employing the formula 
V A 2 
® = Y+cV® ' c near ty e T ua l 0-000034 ip within those limits. 
(5) It is difficult to account for the rapid diminution of resistance between 1100 
and 1000 feet. It may be that after the projectile passes below 1100 feet velocity, 
the front part is relieved from extra pressure by permitting the air to run in behind, 
and so fill up the partial vacuum in rear of the shot, 
R = radius of shot, W = weight of shot. 
* See Traits de Balistique experimentale par Hdlie, Professeur a l’Ecole d’Artillerie de la 
Marine. Paris, 1865; 
will nearly equal 0-000063 ^ within those limits. 
