MAGNUS ON THE DEVIATION OF PROJECTILES. 211 



Nevertheless, although since Robins many attempts have 

 been made to explain how, by such a rotation, a deviation of the 

 projectile could be caused, all endeavours, even those of Euler 

 and Poisson, have been fruitless. The latter more particularly 

 treated the subject at great length in several memoirs read before 

 the Paris Academy, which were printed in the Journal de VEcole 

 Polytechnique, and which appeared also in a separate treatise, 

 entitled Recherches sur le mouvement des projectiles dans Vair, 

 Therein he considered, first, the influence of the earth^s revo- 

 lution on the course of the projectile; afterwards, that exercised 

 by the friction of the air on its translatory as well as on its rota- 

 tory motion ; and lastly, that caused by the imperfect sphericity 

 and homogeneity of the mass. From his calculations he con- 

 cluded, that although a deviation is certainly caused by the 

 rotation of the projectile, yet the same is so small that the ob- 

 served deflections cannot be produced'by a friction of the surface 

 against the circumjacent stratum of air*. 



Since then various controversies on the cause of this deviation 

 have taken place, to examine which, however, is not the pur- 

 pose of the present memoir. The insufficiency of all former 

 explanations is thus plainly asserted by M. von Heim, a major 

 in the Wiirtemberg Artillery, in his Beitragen zur Ballislik 

 in besonderer Beziehung auf die Umdrehung der Artilleriege- 

 schosse. At page 13 he says, " To give an explanation of the 

 above-named paradoxical phaenomena w^hich shall be satisfac- 

 tory to the demands of science, is consequently a problem by 

 no means yet solved/' 



An investigation on the motion of fluids, made by me some 

 time ago, suggested the present • explanation of this interesting 

 phaenomenon, which, although differing materially from those 

 heretofore given, appears to me to be the correct one. 



To establish the same, it appeared desirable to examine the 

 subject more closely, and more especially to investigate, by ex- 

 periments on a small scale, the pressure which the air exerts 

 on the several parts of the projectile. 



• In these experiments I have assumed throughout that all rela- 

 tions of pressure are identical, whether the sphere move through 

 the air, or remaining in the same place, the air move against it, 

 * Recherches sur le mouvement des projectiles, p. 77, 



