86 TRANSACTIONS OF THE [JaN. 30 



Service Institution " in 18()9, by A. H. Lane Fox, who, by the 

 ■way, is the same personality as Pitt Rivers, F. R. S , already 

 quoted, correctl}' states one of the principles of action in the 

 boomerang as parallelism of axis. This was, however, first 

 published I believe by an American, Prof. Snell of Amherst, in 

 1855, in a lecture on "Planetary Disturbances," in which he said: 



" We find an elegant illustration of this tendency to parallel- 

 ism of axis in the boomerang." 



But "Parallelism of Axis" is a condition of free motion, and 

 so we are brought to consider the elements of artificially applied 

 force and motion as something of the very first importance. 

 And here we confront another surprising fact in the literature 

 of the boomerang, viz., no mechanical means of any kind, so 

 far as I can find, has hitherto been devised to make repeated 

 projections under similar conditions as crucial tests. 



Evidently, then, the first stej) to be taken was to supply this 

 deficiency. The usual lecture-room expedient of striking a 

 cardboard boomerang from the side of a book, is against good 

 mechanical principles for obtaining extended flights. The 

 mechanism should stimulate the action of the human arm — the 

 most perfect catapult ever devised — but unlike the arm its 

 motive power must be subject to being held indefinitely to the 

 same line on a graduated scale. Such, in a general way, I 

 decided in my mind, should be the characteristics of a machine 

 to make tests. 



The next step was to adapt the details of construction to the 

 theoretically best form of missile. But that form had first to 

 be determined. Theorj^ alone, unaided by additional experi- 

 ment, finds reasons (as will be apparent) to decide against the 

 necessity of either a screw-shape warp or twist or convex upper 

 surface. So, to make a first experiment, I went to a planing 

 mill and selected a thin, hard maple board, and had it planed 

 down to an even thickness. The thought struck me that possibly 

 the cycloidal curve for advancing outline would cause the 

 minimum of air resistance. I constructed a slightly prolate 

 cycloid, with a centroid of 4^^ inches, giving me an outline of 

 about 16 inches. Instead of ending the curve abruptl}' at the 

 base line, I added a spur to each end below the line, shai^ed 

 somewhat like the prow of a boat. This received no secret 

 touch in making. A prosaic jig-saw shaped it and left its edges 

 square and rough . I sharpened the pioneer edges slightly to 

 better cleave the air, taking care not to disturb the cycloidal 

 outline of the under or bearing surface. As a precaution 

 against being warped or twisted by exj)osure I soaked it in oil 

 .and turpentine, and varnished it. 



