C48 THE PRINCIPLES OF SCIENCE. [chap. 



remain in tlie same state of horizontal motion commu- 

 nicated to it by the mast. As the anti-Copernicans had 

 assumed the contrary result as certain to ensue, their 

 avf^ument would of course have fallen through. Had the 

 Copernicans next proceeded to test with great care the other 

 assertion involved, they would have become still better 

 convinced of the truth of their own theory. A stone 

 dropped from the top of a high tower, or into a deep well, 

 would certainly not have been deflected from the vertical 

 direction in 'the considerable degree required to agree with 

 the supposed consequences of the Copernican views ; but, 

 with very accurate observation, they might have discovered, 

 as Benzenherg subsequently did, a very small deflection 

 towards tlie east, showing that the eastward velocity is 

 greater at the top than tlie bottom. Had the Copernicans 

 then l)een able to detect and interpret the meaning of the 

 small divergence thus arising, they would have found in it 

 corroboration of their own views. 



Multitudes of cases might be cited in which laws of 

 nature seem to be evidently broken, but in which the 

 ap])arent breach arises from a misapprehension of the case. 

 It is a general law, absolutely true of all crystals yet sub- 

 mitted to examination, that no crystal has a re-entrant 

 angle, that is an angle which towards the axis of the crystal 

 16 greater than two right angles. Wherever the faces of a 

 crystal meet they produce a projecting edge, and wherever 

 edges meet they produce a corner. Many crystals, however, 

 wlien carelessly examined, present exceptions to this law, 

 but closer observation always shows that the apparently 

 re-entrant angle really arises from the oblique union of two 

 distinct crystals. Other crystals seem to possess faces 

 contradicting all the principles of crystallography ; but 

 careful examination shows that the supposed fjices are not 

 true faces, but surfaces produced by the orderly junction 

 of an immense number of distinct thin crystalline plates, 

 each plate being in fact a separate crystal, in which the 

 laws of crystallography are strictly observed. The rough- 

 ness of the supposed face, the striae detected by the 

 microscope, or inference by continuity from other specimens 

 where the true faces of the plates are clearly seen, prove the 

 mistaken character of the sujiposed exceptions. Again, four 

 of the faces of a regular octahedron may become so enlarged 



