THE TEACHING OF MECHANICS BY EXPERIMENT. 251 
the testing machine and the experimental engine and boiler, though 
these were often supplemented by other appliances dealing with 
special problems in applied mechanics. Both these two lines of work 
have a very direct practical bearing on the questions with which an 
engineer has to deal professionally, and they naturally continue to 
take a conspicuous place in the scheme of any engineering laboratory. 
But I wish to speak to-day of other experiments of a less highly 
specialized kind, experiments which are useful not only to engineers, 
but to all students who wish to gain clear concrete conceptions of 
what mechanical principles really mean. 
Broadly speaking, there are two ways of treating the science of 
mechanics. One way is to regard it merely as an exercise in mathe¬ 
matical deduction. The other way is to regard it as a means of 
solving real problems presented by real things. 
In either case you start from certain first principles, which are 
fruits of experience, principles such as Newton formulated in his 
three laws. But after that the purely mathematical student of 
mechanics leaves experience severely alone. He concerns himself 
only with mathematical 'deductions, lives in an ideal world of inex- 
tensible strings and smooth pegs, and if he ever comes near enough to 
reality to sketch a screw it is such a screw as was never seen out of a 
text-book. 
On the other hand if you approach the science of mechanics from 
the stand-point of the engineer, it is your endeavour, at every point of 
the logical process, to keep in touch with real things. The science is 
no less a logical deduction from first principles, but every step is felt 
to be an advance in the comprehension of matters of every-day 
experience. As the student pursues his study he remains consciously 
and continuously in the world of sense. He expressly avoids soaring 
into the cloudland of abstractions. 
To my thinking, this is the better way, and there can at least be no 
doubt that for the engineer and for the artillery officer it is the only 
rational way. Experiment forms a powerful aid in this method of 
studying mechanics. 
The title of my lecture must not be understood to imply that exper¬ 
iment is anything more than an aid in that study. I do not mean 
that it is through experiment that the truths of mechanics are to be 
learnt. No one would endeavour to establish the truth of the principle 
of the triangle of forces by pulling a body with two strings and then 
finding how a third string must pull to produce equilibrium. But a 
simple experiment such as that is of value in fixing the principle in 
our minds and in making us realise that it has application to common 
things. And the argument for experiment becomes stronger when 
the mechanical principle involved is of a more recondite kind. Ex¬ 
periments in mechanics illuminate the subject by acting as an aid to 
the imagination. They supplement the fruits of experience to which, 
consciously or not, the student of statics and dynamics naturally refers 
for the support and illustration of his deductions. 
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