480 wherry: classes of crystals 



not compulsory and may be altered in accordance with her own 

 desires. 



Therefore, if she becomes conscious that a projectile intended 

 for her is on the way, she is in a position to baffle all the cal- 

 culations of w^hich this projectile is the unconscious carrier. 

 ■ What, then, is any observation w^orth, e*ven though it be 

 minutely exact, that the gunner can figure out in regard to the 

 deviations between his points of burst and the objective? To 

 what extent do these deviations indicate an error of fii-ing which 

 is subject to rectification? To what extent are they the effect of 

 ^ modification in the continuity of the flight of the objective, 

 voluntarily brought about by the pilot during the course of the 

 projectile? 



The first burst that will take place and which the pilot will 

 see will give him the alarm and from this moment on, what 

 craftiness, what feat of strength in case of need, will he not 

 make use of in order to avoid falling into the net of subsequent 

 trajectories? 



Are not these points of interrogation sufficient to make it 

 clearly understood that the systems of anti-aircraft firing based 

 solely on ranging must be condemned as being ineffective and 

 excessively expensive? 



Are they not sufficient to show that so long as there shall 

 not have b'een found a gun of a fantastic muzzle velocity, capa- 

 ble of pouring into space projectiles of a speed infinitely supe- 

 rior to that of the flying machine, the gunner must concentrate 

 all his attention and all his ingenuity in operating sudden and 

 dense barrages on points of extrapolation silently determined 

 by measurements as accurate as possible? 



CRYSTALLOGRAPHY. — The assignment of crystals to syin- 

 metry classes. Edgar T. Wherry, Bureau of Chemistry. 



The thirty-two classes of crystals are founded on sd firm a 

 basis that it has become customary to regard the assignment of a 

 crystallized substance to one or the other of them as one of the 

 fundamental aims of crystallography. Evidence has been ac- 

 cumulating for some time, however, that certain substances are 

 in a sense intermediate between classes, possessing simultaneously 



