1892.] 229 [Bache. 



Explanation of Plates. 



Plate VII. 



Fig. 1. Holonema horrida Cope ; lateral ventral plate ; Iwo-tbirds natural 



size. 

 Fig. 2. Holonema rugosa Claypole ; lateral ventral plate ; one-half natural 



size. 

 Fig. 3. Holoptychias filosus Cope; scale; two- thirds natural size. 



Plate VIII. 



Megali:hthys macropomus Cope ; skull from above ; about three-fourths 

 natural size ; from the collection of R. D. Lacoe. 



Civil and Military Photogrammetry. 



By R. Meade Bache. 



(^Read before the American Philosophical Society, Afay 6, i8g2.') 



Photogrammetry is recognized as a legitimate mode of survey- 

 ing. It is, in fact, if practiced with due regard to the limitations 

 involved through spherical aberration from object-glasses of too 

 wide aperture, a mode of surveying of considerable accuracy, 

 although not for a moment to be compared to other perfected 

 modes of the present day. It can never rival these in their sphere, 

 which is the sphere of extreme precision, but at the same time it 

 must be admitted that, within its own, it is capable of doing good 

 service. 



The diagram on the blackboard has been made as simple as 

 possible, to illustrate the mode of obtaining a single vertical and a 

 single horizontal determination. It is evident, however, that the 

 sectors of horizon and intervening landscape belonging to each 

 picture, assumed to have been taken from the respective stations, 

 A and B, might be filled with objects. Many of these, from the 

 fact of their having been visible from both stations, would be 

 determinable by this method of cartography. 



AB is a base to serve for the determination of some of the details 

 of a survey. The optical axis of the camera being set at each sta- 

 tion respectively upon a prominent, distant object, say a lone tree, 

 the angle at each station between the base and that object is taken. 



