540 



NA TURE 



[August i, 1901 



the horizon of the initial velocity of translation) must be com- 

 parable with 45°. 



The uphill path is nearly straight until the forward velocity 

 becomes small ; the projectile then returns along a track close 

 to that of the ascent tFigs. 12 and 13). 



Non-reliirning Jiiglits. — A good boomerang of the second 

 type will travel an immense distance in a nearly straight line if 

 properly thrown. The motion should resemble that of an aero- 

 plane or flying machine ; the plane of rotation must remain 

 nearly horizontal though slightly uphill, and the trajectory must 

 be flat. There will thus be an upward pressure of air on the 

 under surface of the implement, and the force of gravity will be 

 counteracted as long as there is sufficient forward velocity. The 

 boomerang is thrown very slightly uphill, the angle of projection 

 not being greater than 12" ; the rounded side is uppermost and 

 e is initially 30". The plane of rotation soon appears to the 

 thrower to become approximately horizontal, and it remains so 

 during the flight ; the projectile rises to a height of about 12m. 

 from the ground and travels in a nearly straight path until its 

 forward velocity is almost exhausted ; it then strikes the earth 

 at a distance of about 130 metres from the thrower. 



It will be seen that the angular velocity (i) is at first small and 

 positive, and that it subsequently disappears ; the angular 

 velocity (2) is small throughout. These results are due to the 

 left-handed twist and the rounding. 



Considerable accuracy both in making and in throwing 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 be bent 

 and materially shortened. The correct relation has to be found 

 between the twist, the rounding, the angle between the arms of 



Fig. 12. —Plan. 



-Elevation through AC 



the boomerang, the density of its material, and the amounts and 

 directions of its initial linear and angular velocities. An illus- 

 tration of this is afforded by the first specimen of this type that 

 I have made ; it travels further against the wind than with it. 

 In the former case the boomerang keeps quite low, scarcely 

 rising higher than 6 metres, and, being retarded very little by 

 frictional resistance, travels about 125 metres ; in the latter case 

 the body spends its energy in running uphill to a height of about 

 15 metres, and falls to the ground at a distance of about 90 

 metres. 



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 grammes weight of copper wire 

 in three equal portions, of which one is in the middle and one 

 near each end. This materially increases the moment of inertia 

 about the centre of gravity without interfering seriously with 

 other details. I have thrown a loaded boomerang of this type 

 167 metres, and my range with a spherical ball of half the weight 

 is only 63 metres. 



JModeof inanufactuye. — A block of straight-grained ash about 

 90 cm. long, 7 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 sirip.s 1-3 cm. thick. After sufficient time has 

 lapsed 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 any rate in the 

 neighbourhood of the bend, should follow the grain of the wood. 

 When the projectile falls hard upon one end the stress near the 

 centre is very severe, and any point at which the direction of 



NO. 1657, VOL. 64] 



the grain meets the convex edge obliquely is likely to develop a 

 split and ultimately a breakage. 



It is better to cut the material to its final twisted shape rather 

 than to impart the twist by another steaming and bending. 

 Considerable care is required in the process, for the removal of 

 a layer of wood a millimetre thick in such a way as to increase 

 or diminish the twist will cause a marked difference in the 

 flight. It will be found to facilitate throwing to cut that end of 

 the boomerang which is held in the hand to the somewhat 

 square form shown at the right hand of Figs, i and 3. 



There is some difficulty in avoiding warping, for boomerangs 

 are less likely to get broken if thrown when the ground is damp 

 and soft, and under these circumstances the moisture is likely 

 to be absorbed by the wood. It is of great advantage, therefore, 

 to make the surface of the implements very smooth with fine 

 glass-paper and to saturate them with linseed oil. The 

 additional density thereby produced is also of service in that it 

 diminishes the effect of the frictional resistance of the air. 



I have used artificially bent oak as a material, but have not 

 found it as heavy or as strong as ash. Oak branches that are 

 naturally bent are not hard to procure, but boomerangs made 

 from them are liable to break at places where there are knots or 

 irregularities in the grain of the wood. 



Evolution. — Boomerangs of every variety of shape are still to 

 be found in Australia, and it appears impossible to get direct 

 historical evidence as to the nature of the successive .stages of 

 development. But if speculation be allowed, the following 

 series may be suggested. 



First we should have a clumsy kind of wooden sword, curved, 

 but without rounding or twist, and with one end roughened 

 to form a handle ; when the intended victim was out of reach 

 it would be natural to throw the weapon, and at short ranges it 

 would be extremely effective. Bad workmanship would involve 

 the frequent production of implements of which one side was 

 more rounded than the other, and it would soon be found that 

 these missiles, when thrown wiih the rounded side uppermost, 

 travelled much further and straighter than the former. 



Boomerangs of this character vary in length from 50 to no 

 cm., and in weight from 200 grammes to 1250. They ate, for 

 the most part, twisted in a manner that seems quite fortuitous, 

 and form the enormous majority of the present native imple- 

 ments. Light specimens with a slight lefi-handed twist may 

 have a fairly straight trajectory of loo metres, and may return 

 if aimed much uphill, especially when thrown against a wind. 

 Those which are bent through a large enough angle and happen 

 to be twisted {either by carelessness in manufacture or by sub- 

 sequent warping ') after the manner of a right-handed screw are 

 returning boomerangs of the first type. In many of these the 

 twist is so large as to be conspicuous, and when once the con- 

 nection between the form and the return flight has been noticed, 

 the process of development is complete. 



Gilbert T. Walker. 



THE INTERNATIONAL SEISMOLOGICAL 

 CONFERENCE AT STRASSBURG. 

 TN 1895 the late Dr. Rebeur-Paschwitz proposed, with the 

 ■'• approval of Prof. Milne and other seismologists, to form an 

 international seismological union. Although, unfortunately, he 

 did not live to carry the project into execution, the micro- 

 seismic survey of the world has since then been actively pushed 

 on by Prof. Milne, the observatories using the Milne horizontal 

 pendulums now numbering about forty. Meanwhile, the pro- 

 ject of Rebeur-Paschwitz was taken up by Prof. Gerland, and, 

 thanks to his active exertions, the first international seismo- 

 logical conference was finally held at Strassburg on April 11- 

 13^ The total number of the members who attended the con- 

 ference was thirty-five, as follows ■.—Austria- Hungary (Prof. 

 Belar, Prof. Exner, Prof, von Kovesligethy, Hofrath Konkoly, 

 Prof. L.iska, Prof. Schafarzik) ; Belgium (Prof. Langrange) ; 

 Denmark (Lieutenant-Colonel Harboe) ; Germany (Dr. Ebell, 

 Dr. Ehrismann, Prof. Futierer, Prof. Gerland, Prof. Giinther, 

 Dr Hecker, Prof. Helmert, Herr Jaehnike, Prof. Kobold, 

 Geheimralh Lewald,Prof. Leutz, Prof. Rudolph, Dr. Polls, Prof. 

 Schmidt, Dr. Schiitt, Prof. Straubel, Dr. Tetens, Prof. Wagner, 

 Prof. Weigand, Prof. Wiechert); Italy (Dr. Oddone) ; /a/a;/ 



1 This may be illustrated by the fact ihat when the author first made 

 boomerangs he was only aware of the need lor rounding : but the first two 

 specimens that he constructed happened to have nght-handed twist and 

 returned admirably. 



