66 JOURNAL OF THE 



push toward the bird. The corresponding amount of air would 

 be lost at the tip of the other wing, and would work to coun- 

 teract the sideways thrust of the first one mentioned. This 

 amount of air beside being lost would actually work to the an- 

 noyance of the bird. Work would be performed only by one 

 primary, whereas, with the primaries separated, all work, and all 

 of the air is utilized. The value of the separation can be seen 

 when we consider the amount of air which passes out at the end 

 of such a large compressing surface, and especially when we 

 note in soaring the distal ends of the bird's wings are slightly 

 elevated. 



It is difficult to conceive how Mr. Trowbridge could mistake 

 this natural emargination of the primaries of soaring birds* for 

 a wearing produced by a supposed artificial overlapping of these 

 primaries to which the bird had recourse in soaring. Were it 

 possible for such a bird to lock its primaries into a compact sur- 

 face, it could not soar so readily as when the primaries w T ere in 

 their natural position. 



OF THE THREE CRYSTALLOGRAPHIC AXES. 



\VM. B. PHILLIPS. 



The study of Crystallography is considered by most young 

 students as something of a bugbear. This view of a really 

 beautiful study is perhaps not unnatural. So short a time is 

 devoted to it in most colleges that opportunity is not given for 

 the proper unfolding of it. 



During the course in Mineralogy as offered in the University 

 of North Carolina for the past two years the greatest difficulty 

 that has been met is in the almost total lack of training in the 



^Science, Nov. 18, 1887, Jan. 6, 1888. 



