BOOMERANGS. 519 



though sliohtl}' uphill, and the tnijectorv nuist he flat. There will 

 thu.s be an upward pressure of air on the under surfaee of the imple- 

 ment, and the force of gravity will he counteracted as long- as there is 

 sufficient forward velocity. The boomerang i.s thrown very slightly 

 uphill, the angle of projection not beino- greater than 12 ; the rounded 

 side is uppermost and ^ is initially 'MP. The plane of rotation soon 

 appears to the thi'ower to become approximately horizontal, and it 

 remains so during the flight; the inojectile rises to a height of about 

 12 meters from the ground suid travels in a nearly straight path until 

 its forward velocity is almost exhausted; it then strikes the earth at a 

 disttmce of about 130 meters from the thrower. 



It will be seen that the angular velocity (1) is at first small and posi- 

 tive, and that it subsequently disappears; the angular velocitv (2) is 

 siuall throughout. These results are due to the left-handed twist and 

 the rounding. 



Considerable accui'acy, both in making and in throv.ing, is necessary 

 if the best results are to be obtained. If the plane of rotation slopes 

 downward to one side, the boomerang will slide down in the inclined 

 plane of rotation; thus the path will ])e bent and materially shortened. 

 The correct relation has to be found lietween the twist, the rounding, 

 the angle between the arms of the boomerang, the density of its 

 material, and the amounts and directions of its initial linear and angu- 

 lar velocities. An illustration of this is afforded bj' the first specimen 

 of this type that I have made: it travels farther against the wind than 

 with it. In the former case the boomerang keeps quite low, scarcely 

 rising higher than 6 meters, and being retarded very little by f rictional 

 resistance, travels about 12.5 meters; in the latter case the body spends 

 its energy in running uphill to a height of about 15 meters, and falls 

 to the ground at a distance of about 90 meters. 



It is rather difficult to give sufficient spin to keep the motion stable 

 through a long flight, and I have found it advantageous to wind round 

 the wood about 60 grams weight of copper wire in thi'ee equal por- 

 tions, of which one is in the middle and one near each end. This 

 materiallv increases the moment of inertia aliout the center of gravit\' 

 without interfering seriously with other details. I have thrown a 

 loaded boomerang of this type 107 meters, and my range with a spher- 

 ical ball of half the weight is onh' 03 meters. 



MODE OF MANUFACTURE. 



A block of straight-grained ash about 90 cm. long. T cm. (or 7.5 cm.) 

 thick, and of width not less than 7 cm., is taken. The block is soaked 

 in steam, bent to the requisite shape and held in this shape until cool 

 and dry. It is then sawn into strips 1.3 cm. thick. After suffi(;ient 

 time has elapsed for the wood to be seasoned, each strip is trimmed into 

 a boomerang, the most useful tool in general being a spokeshave. It 

 is very important that the outer edge, at an}' rate in the neighborhood 



