569 



TEANSACTIONS OF THE SECTIONS. 



Section A.— MATHEMATICAL AND PHYSICAL SCIENCE. 



President of the Section — Professor Sir R. S. Ball, M.A., LL.D., F.K.S., 

 F.R.A.S., M.R.I. A., Astronomer Royal for Ireland. 



THURSDAY, SEPTEMBER 1. 



The PeeSident delivered the following Address : — 



A Dynamical Parable. 



Ladies and Gentlemen, — The subject I have chosen for my address to you to-day 

 has been to me a favourite topic of meditation for many years. It is that part of 

 the science of theoretical mechanics which is usually known as the ' Theory of 

 Screws.' 



A ^ood deal has been already written on this theorj', but I may say with some 

 confidence that the aspect in which I shall invite you now to look at it is a novel 

 one. I propose to give an account of the proceedings of a committee appointed to 

 investigate and experiment upon certain dynamical phenomena. It may appear 

 to you that the experiments I shall describe have not as yet been made, that even 

 the committee itself has not as yet been called together. I have accordingly 

 ventured to call this address ' A Dynamical Parable.' 



There was once a rigid body which lay peacefully at rest. A committee of 

 natural philosophers was appointed to make an experimental and rational inquiry 

 into the dynamics of that body. The committee received special instructions. 

 They were to find out why the body remained at rest, notwithstanding that 

 certain forces were in action. They were to apply impulsive forces and observe 

 how the body would begin to move. They were also to investigate the small 



oscillations. These being settled, they were then to But here the chairman 



interposed ; he considered that for the present, at least, there was sufficient work 

 in prospect. He pointed out how the questions already proposed just completed a 

 natural group. ' Let it suffice for us,' he said, * to experiment upon the dj'namics 

 of this body so long as it remains in or near to the position it now occupies. 

 We may leave to some more ambitious committee the task of following the body 

 in all conceivable gyrations through the universe.' 



The committee was judiciously chosen. Mr. Anhannonic undertook the 

 geometry. He was found to be of the utmost value in the more delicate parts of 

 the work, though his colleagues thought him rather prosy at times. He was much 

 aided by his two friends, Mr. One-to-One, who had charge of the homographic 

 department, and Mr. Helix, whose labours will be seen to be of much importance. 

 As a most respectable, if rather old-fashioned member, Mr. Cartesian was added to 

 the committee, but his antiquated tactics were quite out-manceuvred by those of 

 Helix and Oue-to-One. I need only mention two more names. Mr. Commonsense 

 was, of course, present as an ex-officio member, and valuable service was even 

 rendered by Mr. Querulous, who objected at first to serve on the committee at all. 



