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 miles an hour? He would have been told that such predictions "could only have originated from an imperfect comprehension of the problems involved." But we know that they would have been perfectly sound, though it would have been difficult to withhold assent from the derision which instructed hearers would have poured upon them. The effect of any scientific discovery can only be measured when we are in a position to judge of the conditions in which it may be applied, and the further discoveries which may affect it—a consideration which will help us against the danger of undue caution in estimating the possible developments of recent discovery when utilised in the conditions of the next century and reinforced by inventions and discoveries yet to come.

A like caution will, however, teach us to restrain our expectations from the new knowledge which radium appears to be gradually unfolding, not because there is any doubt that radio-activity will ultimately bring priceless gifts to civilisation, but because in our present ignorance of all but a few facts concerning it we can form no possible conjecture as to the lines these gifts will follow. Already we seem to have seen in some of the radium experiments one "element" turn into another. If this should develop until we acquire the power which used to be dreamed of as transmutation,