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1855.] to associate gravity with them; and perhaps enable us to know whether the essential force of gravitation (and other attractions)is internal or external as respects the attracted bodies.

Returning once more to the definition of the gravitating power as "a simple attractive force exerted between any two or all the particles or masses qf matter at every sensible distance, but with a STRENGTH VARYING inversely as the square of the distance," I ought perhaps to suppose there are many who accept this as a true and sufficient description of the force, and who therefore, in relation to it, deny the principle of conservation. If both are accepted and are thought to be consistent with each other, it cannot be difficult to add words which shall make "varying strength" and "conservation" agree together. It cannot be said that the definition merely applies to the effects of gravitation as far as we know them. So understood, it would form no barrier to progress; for, that particles at different distances are urged towards each other with a power varying inversely as the square of the distance, is a truth; but the definition has not that meaning; and what I object to is the pretence of knowledge which the definition sets up, when it assumes to describe, not the partial effects of the force, but the nature of the force as a whole. June, 1858.

Observations on Mental Education.

These observations were delivered as a lecture before His Royal Highness The Prince Consort and the Members of the Royal Institution on the 6th of May, 1854. They are so immediately connected in their nature and origin with my own experimental life, considered either as cause or consequence, that I have thought the close of this volume not an unit place for their reproduction] courage, Sir, from your presence here this day, to speak boldly that which is upon my mind. I feared that it