41G JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 17 



may be advantageous. For regularly shaped cellular tubes, with 

 straight walls, parallel to the wind, and with no vanes or holes, an 

 empirical formula was developed which was found to express air 

 flow through the core in terms of flying speed, with a surprising de- 

 gree of accuracy : 



M — 10 ^ ) 



ni = a [1 



where r is hydraulic radius of an air tube (quotient of cross section 

 by perimeter) and % is depth of the core (length of an air tube) , both 

 these dimensions being measured in the same unit of length; a (the 

 free area of the core) is the ratio of the total cross sectional area of 

 the air tubes in a given frontal area to that frontal area; m is the 

 air flow constant, the fractional part of the air flow approaching the 

 core which passes through it, hence, unity minus the fractional part 

 deflected around the core. In a wind stream of 5 pounds per second 

 per unit area, a core of unit frontal area which transmitted 3 pounds 

 of air per second and deflected the other 2 around it, would have an 

 air flow constant of 0.60. The presence of headers or water boxes 

 would modify the direct application of the formula to a radiator since 

 the formula is for a core alone, but with the exercise of suitable judg- 

 ment in making an allowance for water boxes and connection piping, 

 it should be possible, from the geometrical characteristics of a simple 

 core, to compute with a satisfactory degree of accuracy the air flow 

 which would correspond to any stated flying speed with the core in an 

 unobstructed position. 



ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably prepared and 

 signed by themselves, are forwarded promptly to the editors. The abstracts should con- 

 form in length and general style to those appearing in this issue. 



GEODESY. — Radio-compass bearings. Oscar S. Adams. U. S. Coast 

 and Geodetic Survey vSpec. Publ. 75. (Serial 167.) Pp. 39. 1921. 



The radio-compass is coming into very general use for the determination 

 of the positions of vessels at sea. For this reason, it seemed advisable to 

 investigate the methods of plotting bearings thus obtained, both on the Mer- 

 cator projection and on the gnomonic projection. In investigating the subject 

 it is sufficiently exact to consider the earth as a sphere. It is further as- 

 sumed that the path of the wireless wave over the surface of the earth is a 

 great circle, joining the position of the vessel with that of the radio-compass 

 station. 



A straight line on a Mercator projection represents a rhumb line and not a 

 great circle. A great circle on this projection is represented by a curve 



