106 MECHANICAL RECREATIONS fcH. V 



additional complications are introduced by the fact that the 

 velocities of translation and rotation are retarded at different 

 rates and that usually there will be some wind blowing in 

 a cross direction. But generally we may say that the effect of 

 the under-cut given by a normal stroke is to cause the ball 

 to rise, and therefore to lengthen the carry. Also, if a wind is 

 blowing across the line to the hole from right to left, a drive, if 

 the player desires a long carry and has sufficient command over 

 his club, should be pulled ; but an approach shot, if it is desired 

 that the ball should fall dead, should be sliced because then the 

 ball as soon as it meets the wind will tend to fall dead. Con- 

 versely, if the wind is blowing across the course from left to 

 right, the drive should be sliced if a long carry is desired, and 

 an approach shot should be pulled if it is desired that the ball 

 should fall dead. 



The questions involving the application of Hauksbee's Law 

 are easy as compared with many of the problems in fluid motion. 

 The analysis required to attack most of these problems is beyond 

 the scope of this book, but one of them may be worth mentioning 

 even though no explanation is given. 



The Theory of the Flight of Birds. A mechanical problem of 

 great interest is the explanation of the means by which birds are 

 enabled to fly for considerable distances with no (perceptible) 

 motion of the wings. Albatrosses, to take an instance of special 

 difficulty, have been known to follow for some days ships sailing 

 at the rate of nine or ten knots, and sometimes for considerable 

 periods there is no motion of the wings or body which can 

 be detected, while even if the bird moved its wings it is not 

 easy to understand how it has the muscular energy to propel 

 itself so rapidly and for such a length of time. Of this 

 phenomenon various explanations* have been suggested. 

 Notable among these are Sir Hiram Maxim's of upward air- 

 currents, Lord Rayleigh's of variations of the wind velocity at 

 different heights above the ground, Dr S. P. Langley's of the 



* See G. H. Bryan in the Transactions of the British Association for 1896, 

 vol. lxvi, pp. 726—728. 



