86 TRANSACTIONS OF THE [JAN. 30 
Service Institution’’ in 1869, by A. H. Lane Fox, who, by the 
way, is the same personality as Pitt Rivers, F. R. S, already 
quoted, correctly 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 applhed 
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 step 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 haman 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. Theory 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 41% inches, giving me an outline of 
about 16 inches. Instead of ending the curve abruptly at the 
base line, I added a spur to each end below the line, shaped 
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 exposure I soaked it in oil 
and turpentine, and varnished it. 
