60 Mr. J. W. Sharpe : 



o£ temperature. The experiments of Rutherford and Soddy * 

 show that this is the case. 



The existence of " de-emanated " products after strong- 

 ignition whereby many physical and chemical properties of 

 the compound are changed, can be also explained by the 

 change in dissolving power of these compounds. Further 

 investigations will show if this generalization of the fact 

 observed in the case of uranium is justifiable. 



Further experiments on this subject are in progress. 

 Analogous experiments will also be tried with other radioactive 

 products in order to see whether this explanation is general. 



In conclusion I wish to express my best thanks to Prof. 

 Rutherford for the interest he took in this work and for the 

 encouragement I received from him. 



McGill University, Physics Building, 

 April 3, 1905. 



VII. The Boomerang. By J. W. Sharpe, M.A.\ 



IT is easy to show in what manner the leading peculiarities 

 of the boomerang's motion depend upon fundamental 

 dynamical principles. 



Though the instrument is not perfectly flat, it will be con- 

 venient to use the term " principal plane " for its average 

 plane. The C.G. is somewhere within the concavity, and 

 the two horns are symmetrically disposed with regard to it. 

 The normal through the C.G. to the principal plane will be 

 called the axis of the boomerang. The three principal axes 

 of inertia at the C.G. are one along this axis (this one has 

 the maximum moment of inertia), and two others in the 

 principal plane, respectively parallel and perpendicular to 

 the line joining the horns. 



Imagine the boomerang held in the right hand, upright, 

 with the concave edge forward and the principal plane 

 vertical, which is in fact the ordinary posture for making a 

 returning throw. The surfaces are both slightly convex, the 

 one next the thrower (to be called throughout the motion the 

 " upper" surface) being always the more curved one of the two. 

 Also the whole instrument has a slight twist in it, so that the 

 " upper " side of the upper horn and the " lower " side of 

 the lower horn are slightly turned towards, and facing, the 

 thrower. This twist is such as to make the boomerang screw 

 itself upwards in the air when thrown with its principal 

 plane horizontal instead of vertical. Its bent form has the 



* Rutherford and Soddy, Phil. Mag. April 1903, p. 453. 

 t Communicated bv the Author. 



