14 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGJ 



VOL. 



ABBREVIATIONS ANI> SYMBOLS EMPLOYED 



The following rules and symbols were adopted for determining the relative 

 position of points on the aerodrome, some of them during L891, and some of 

 them since. All arc given here for convenience of reference, though their chief 

 application is to the larger steam aerodromes described later. Those which im 

 mediately follow were meant to give some of the notation of descriptive geomel rj 

 in untechnical language for the use of the workmen employed. Lei A'. )' and /. 

 be three lines at right angles to each other, and passing through the same point 

 in space, 0, lying at any convenient distance above the floor of the work-shop. 



PlO. 2. Diagram showing mensural coordinates 



The line X lies North and Smith; the line 1' lies Easl and West, and the line Z 

 points to the zenith. Now place the aerodrome on the floor so that its principal 

 axis lies horizontally in the plane XX. with its head pointing North, and in such 

 a position that a line passing through the center of the propellers shall coincide 

 with the line Y. 



When measurements are made on or parallel to the line A, the point ot in 

 tersection will he marked 1500 centimetres, and distances toward the South 

 will he less than, and distances toward the North greater than L500 centimetres. 



When measurements are made on or parallel to the line X. the point will 

 he considered to lte marked iMOn centimetres, and distances above will he greater 



than, and distances below will he less than 2500 < entimetres. 



