so air yields somewhat to pressure.  A ball filled with compressed air bounces better than one filled with anything else; so air is elastic.  Raise your arm horizontally from the water when you are lying in your bath; you will feel a terrible weight on it; so air is a heavy body.  By establishing an equilibrium between air and other fluids its weight can be measured, hence the barometer, the siphon, the air-gun, and the air-pump.  All the laws of statics and hydrostatics are discovered by such rough experiments.  For none of these would I take the child into a physical cabinet; I dislike that array of instruments and apparatus.  The scientific atmosphere destroys science.  Either the child is frightened by these instruments or his attention, which should be fixed on their effects, is distracted by their appearance.

We shall make all our apparatus ourselves, and I would not make it beforehand, but having caught a glimpse of the experiment by chance we mean to invent step by step an instrument for its verification.  I would rather our apparatus was somewhat clumsy and imperfect, but our ideas clear as to what the apparatus ought to be, and the results to be obtained by means of it.  For my first lesson in statics, instead of fetching a balance, I lay a stick across the back of a chair, I measure the two parts when it is balanced; add equal or unequal weights to either end; by pulling or pushing it as required, I find at last that equilibrium is the result of a reciprocal proportion between the amount of the weights and the length of the levers.  Thus my little physicist is ready to rectify a balance before ever he sees one.

Undoubtedly the notions of things thus acquired for oneself are clearer and much more convincing than those acquired from the teaching of others; and not only is our reason not accustomed to a slavish submission to authority, but we develop greater ingenuity in discovering relations, connecting ideas and inventing apparatus, than when we merely accept what is given us and allow our minds to be enfeebled by indifference, like the body of a man whose servants always wait on him, dress him and put on his shoes, whose horse carries him, till he loses the use of his limbs.  Boileau used to boast that he had taught Racine the art of rhyming with difficulty.  Among the many short cuts to science, we badly need some one to teach us the art of learning with difficulty.

The most obvious advantage of these slow and laborious inquiries is this:  the scholar, while engaged in speculative studies, is actively using his body, gaining suppleness of limb, and training his hands to labour so that he will be able to make them useful when he is a man.  Too much apparatus, designed to guide us in our experiments and to supplement the exactness of our senses, makes us neglect to use those senses.  The theodolite makes it unnecessary to estimate the size of angles; the eye which used to judge distances with much precision, trusts to the chain for its measurements; the steel yard dispenses with the need of judging weight by the hand as I used to do.  The more ingenious our apparatus, the coarser and more unskilful are our senses.  We surround ourselves with tools and fail to use those with which nature has provided every one of us.