742 



THE THEOEY OF TRANSFORMATIONS 



[CH. 



toe is a precisely identical function of the form F (e*', y-^ = 0, 

 where x^, y^ are oblique co-ordinate axes inclined to one another 

 at an angle of 50°. 



Fig. 366. (After Albert Durer.) 



Diirer was acquainted with these oblique co-ordinates also, 

 and I have copied two illustrative figures from his book*. 



In Fig. 367 I have sketched the common Copepod Oithona nana, 



Fig. 367. Oithona nana. 



Fig. 368. Sapphirina. 



* It was these very drawings of Diirer's that gave to Peter Camper his notion 

 of the "facial angle." Camper's method of comparison was the very same as em's, 

 save that he only drew the axes, without filling in the network, of his coordinate 

 system ; he saw clearly the essential fact, that the skull varies as a whole, and that 

 the "facial angle" is the index to a general deformation. " The great object was to 

 shew that natural differences might be reduced to rules, of which the direction of 

 the facial line foi'ms the norma or canon; and that these directions and inclinations 

 are always accompanied by correspondent form, size and position of the other 

 parts of the cranium," etc. ; from Dr T. Cogan's preface to Camper's work On the 

 Connexion between the Science, of Anatomy and the Arts of Drawing, Painting and 

 Sculpture (1768?), quoted in Dr R. HamOton's Memoir of Camper, in Lii-es of 

 Eminent Naturalists {Nat. Libr.), Edin. 1840. 



