266 
THE TEACHING- OF MECHANICS BY EXPEEIMENT. 
fore us in this room in a lecture by Dr. Bryan. What would be the effect of 
diluting gravity supposing we could reduce gravity to half its present amount ? 
Would it be possible to fly any easier? Because at the same time the density of 
the air would be halved? It appears that if gravity was reduced from 32 to 16, 
we should still be as far off the possibilities of flight as ever. 
Before the commencement of the lecture Professor Ewing invited me to air 
some of my own heresies. 1 must confess that it gave me secret pleasure to 
hear him begin by describing what was the effect of the addition and the man¬ 
ipulation of certain “ masses ” in connection with his pendulum and gradually by 
some process of transmutation these “ masses ” became “ weights ” as the 
lecture went on. What was the essential difference then between the quantity 
which began by being a £C mass ” and ended by being a “ weight ” ? I saw the 
converse process taking place very rapidly a short time ago during the preparation 
of the Naval Text Book of gunnery. A Captain of the Boyal .Navy was told 
off to prepare this book and when it was completed he had to submit the proofs 
to the Professor of Mathematics at Greenwich Naval College; and back came 
these proofs marked by his censor with every letter, crossed out and re¬ 
placed by the letter “m,” and wherever the word weight occurred—weight 
of gun, shot, and so on, that also was crossed out and the word “ mass ” 
written instead, and the Naval Text Book of Gunnery so appears at the present 
day. I said to the Naval Captain, “ Why did you do this ? we are not going to 
have anything of the kind in our Text Book and the Captain said, “ I do not 
like it myself; supposing I ask the Boatswain what is the mass of the anchor? 
he will think I am starting a theological discussion” (laughter). 
There was a third reason that I was waiting to hear from Professor Ewing for 
the failure of Mr. Squeers’ system of education; I was expecting him to say 
the third reason was the incompetence of his demonstrator, Nicholas Nickleby; 
but I suppose Professor Ewing arrested himself in time, seeing the presence in 
tins room of his late demonstrator, Professor Dunkerley (laughter). 
The Chairman : If no other gentleman wishes to say anything I will make 
a few remarks. 
Professor Ewing in his delightful lecture has given us merely a glimpse of his 
great versatility; he is quite as well known on account of his original work in 
physics as from the fact he is one of our foremost Engineers. The theory of 
magnetic hysteresis and much of the nomenclature and many of the ideas of the 
modern theory of magnetism are due to him. It has been remarked that the 
Professor has designed all the pieces of apparatus, shown and described to us 
this evening, which Cambridge experience has proved to be admirably adapted to 
the purpose of impressing indelibly upon students’ minds the fundamental truths 
of mechanical science. My own experience as a student and teacher has convinced 
me that similar methods of instruction are much wanted in other departments of 
practical mathematics. Solid geometry, hydrostatics and hydrodynamics are 
subjects which it is difficult to learn or teach without models and apparatus. 
In descriptive geometry good models are occasionally found, but they seldom 
teach beyond the elements up to the theory of shadow construction. 
We may gather from the remarks of Professor Ewing and of the speakers who 
followed him that there is a consensus of opinions that theory and practise 
should proceed hand in hand. 
I do not believe we are in danger of seeing experimental methods over done. 
The student cannot appreciate the experiment without a knowledge of its theory 
which is thereby given a reality it could not otherwise possess. If he be an honest 
man the experiment will drive him to the book and the book to the experiment 
until the principles are fixed in his mind. 
