Spinning Tops - by Professor J Perry FRS

 

I picked up this fantastic little book in Cambridge market a few days ago.  Published in 1908 by the Society for the Promotion of Christian Knowledge, it summarizes a lecture performed by Professor J Perry in 1890 in Leeds.

The theme of the Romance of Science series is that remarkable and unexpected things can be discovered from the study of the apparently mundane.  In this lecture Professor Perry performs a series of experiments on various designs of spinning top and shows

i.) What causes the precessional motion of a spinning top

ii.) That a subterranean race could determine that we live on a spinning planet without ever seeing the stars

iii.) Why the precessional motion of a top is in the same orientation as the spin, but the precessional motion of the Earth is in the opposite orientation

iv.) Why some spinning tops stand up when you spin them on their side

and even

v.) A model of how a magnetic field might cause the observed rotation of plane polarized light

The qualitative explanation of precessional motion in a spinning top is vastly more elegant than my attempt using Hamlitonian mechanics. To summarize it:

Imagine a top spinning with an axis of rotation at a slight angle to the vertical.  The force of gravity will tend to make the entire object rotate around a horizontal axis through the pivot at right angles to the spin axis. Axes of rotation can be added like velocity vectors and adding the two results in a new spin axis which looks like the original but rotated slightly around a vertical line through the pivot.

The last page has this romantic and somewhat prescient appeal to the audience to embrace science, and I'm going to quote it here in full (I'm pretty sure copyright has expired by now).

'Imagine the following question set in a school examination paper of 2090 A.D.- "Can you account for the crass ignorance of our forefathers in not being able to see from England what their friends were doing in Australia?" Or this- "Messages are being received every minute from our friends on the planet Mars, and are now being answered: how do you account for our ancestors being utterly ignorant that these messages were occasionally sent to them?" Or this- "What metal is as strong compared with steel as steel is compared with lead? and explain why the discovery of it was not made in Sheffield."

'But there is one question that our descendants will never ask in accents of jocularity, for to their bitter sorrow every man, woman, and child of them will know the answer, and that question is this- "If our ancestors in the matter of coal economy were not quite as ignorant as a baby who takes a penny as equivalent for a half-crown, why did they waste our coal? Why did they destroy what never can be replaced?"

'My friends, let me conclude by impressing upon you the value of knowledge, and the importance of using every opportunity within your reach to increase your own store of it. Many are the glittering things that seem to compete successfully with it, and to exercise a stronger fascination over human hearts. Wealth and rank, fashion and luxury, power and fame-these fire the ambitions of men, and attract myriads of eager worshippers ; but, believe it, they are but poor things in comparison with knowledge, and have no such pure satisfactions to give as those which it is able to bestow. There is no evil thing under the sun which knowledge, when wielded by an earnest and rightly directed will, may not help to purge out and destroy; and there is no man or woman born into this world who has not been given the capacity, not merely to gather in knowledge for his own improvement and delight, but even to add something, however little, to that general stock of knowledge which is the world's best wealth.'

I'd have love to have seen this lecture