414 



SCIENCE 



[N. S. Vol. LIII. No. 1374 



as work done by solution (3) 

 as chemical removal by all agents (1) 

 Comment on these examples is scarcely nec- 

 essary, but it might be added that this list 

 does not by any means exhaust the definitions 

 that might be quoted, as reference to Greg- 

 ory's article will show. 



The definitions suggested by Gregory are 

 as follows: 



denudation =. the wearing down of the land 



by any agency whatever, 

 erosion = the widespread lowering of the 

 land by wind, rain and weather, and by 

 rivers and glaciers acting laterally. 

 corrosion = the excavation by rivers and 



glaciers of their beds, 

 corrasion dismiss as a synonym for corro- 

 sion. 

 These definitions are unsatisfactory in many 

 respects. To separate the lateral and vertical 

 degrading action of rivers and include only 

 the former under the term erosion is not only 

 unnecessary, but highly artificial. Indeed, a 

 satisfactory definition of erosion will be an ex- 

 ceedingly difficult matter to accomplish, for 

 the reason that the word has come to be used 

 in two different senses: one broad sense in 

 which it signifies the general process of the 

 wasting of the land surface and is thus 

 equivalent to denudation, as exemplified in 

 the definition of Davis," and a much narrower 

 sense common in geological literature in such 

 phrases as " ice erosion," " wind erosion," etc. 

 The only solution of this difficulty would ap- 

 pear to be to use " denudation " for the gen- 

 eral process and restrict " erosion " to the 

 narrower meaning of gnawing or cutting 

 away. 



A general term for the action of rivers and 

 glaciers on their banks and beds seems 

 desirable, and for this purpose the word 

 corrasion is much preferable to corrosion, 

 since the latter has a distinctly chemical ira- 

 plieation. There seems to be, on the other 

 hand, no good reason for using separate terms 

 for the lateral and vertical wearing action of 

 streams and glaciers, since the adjectives 

 9 Davis and Snyder, "Physical Geography," p. 

 105. 



lateral and vertical prefixed to corrasion would 

 amply distinguish the two processes. 



There would also appear to be room for the 

 term corrosion as used by Grabau to denote 

 the chemical removal of material by any or 

 all agents, solution being a part of this gen- 

 eral process, and confined to the action of 

 water. 



However these various terms be used even- 

 tually, the need of rescue from the hopeless 

 confusion and ambiguity of the present is un- 

 deniable. The Geological Society of America 

 found it advisable to standardize the nomen- 

 clature of faults; should it not also be the 

 duty of that organization, or, better yet, of an 

 International Congress of Geologists, to take 

 official notice of the ambiguous meanings of 

 the words denudation, erosion, corrasion and 

 corrosion, and establish precise and authora- 

 tative definitions of these much-abused terms ? 

 IVEalcolm H. BissELii 



Brtn Mawe College 



EUCLID OF ALEXANDRIA AND THE BUST OF 

 EUCLID OF MEGARA 



During the middle ages and later, it was 

 the ill fortune of Euclid, the mathematician, 

 to have been confounded with Euclid of 

 Megara who lived about a century earlier and 

 was not a mathematician. As if this confu- 

 sion were not sufficient to tantalize mathe- 

 maticians in general, another mistake came 

 to be made, involving the same two Euclids. 

 This time a bust found on a Greek coin, 

 which according to numismatic authorities is 

 really aimed to represent Euclid of Megara, 

 came to be published broadcast as the picture 

 of the mathematician of Alexandria. This 

 happenfed in England where William Whis- 

 ton, who was Su- Isaac INewton's successor 

 in the Lucasian professorship of matliematics 

 at Cambridge, brought out a school edition of 

 Euclid containing as a frontispiece this bust, 

 said to have been taken from a bronze coin 

 once in the possession of Queen Chi-istina of 

 Sweden.^ Unfortunately this same picture 



1 For the history of Queen Christina's Coin Col- 

 lection, consult an article by Hugo Gaebler in the 



