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TRANSACTIONS OF SECTION A. 315 
If from our explanations and our laws we proceed to prediction, and if the 
* event justifies the prediction through agreement with recorded fact, well and 
good: so far we have a working hypothesis, The significance of working 
hypotheses, in respect of their validity and their relation to causes, is a well- 
known battle-ground of dispute between different schools of philosophers ; it need 
not detain us here and now. On the other hand, when we proceed from our 
explanations and our laws to a prediction, and the prediction in the end does not 
agree with the fact to be recorded, it is the prediction that has to give way. But 
the old facts remain and the new fact is added to them; and so facts grow until 
some working law can be extracted from them. This accumulation of facts is 
only one process in the solution of the universe : when the compelling genius is not 
at hand to transform knowledge into wisdom, useful work can still be done upon 
them by the construction of organised accounts whicl shall give a systematic 
exposition of the results, and shall place them as far as may be in relative 
significance. 
Let me pass from these generalities, which have been suggested to my mind by 
the consideration of some of the scientific changes that have taken place during 
the last hundred years, and let me refer briefly to some of the changes and 
advances which appear to me to be most characteristic of that period. It is not 
that I am concerned with a selection of the most important researches of the 
period. Estimates of relative importance are often little more than half-concealed 
expressions of individual preferences or personal enthusiasms; and though each 
enthusiastic worker, if quite frank in expressing his opinion, would declare his 
own subject to be of supreme importance, he would agree to a compromise that 
the divergence between the different subjects is now so wide as to have destroyed 
any common measure of comparison. My concern is rather with changes, and 
with tendencies where these can be discerned. 
The growth of astronomy has already occupied so large a share of my remarks 
that few more words can be spared here. Not less, but more, remarkable than 
the preceding centuries in the actual exploration of the heavens, which has been 
. facilitated so much by the improvements in instruments and is reinforced to such 
effect by the co-operation of an ever-growing band of American astronomers, the 
century has seen a new astronomy occupy regions undreamt of in the older days. 
New methods have supplemented the old; spectroscopy has developed a science of 
physics within astronomy; and the unastronomical brain reels at the contents 
of the photographic chart of the heavens which is now being constructed by 
international co-operation and will, when completed, attempt to map ten million 
stars (more or less) for the human eye. 
Nor has the progress of physics, alike on the mathematical side and the experi- 
mental side, been less remarkable or more restricted than that of astronomy. The 
elaborate and occasionally fantastic theories of the eighteenth century, in such sub- 
jects as light, heat, even as to matter itself, were rejected in fayour of simpler and 
more comprehensive theories. There was one stage when it seemed as if the mathe- 
matical physicists were gradually overtaking the experimental physicists; but the 
discoveries in electricity begun by Faraday left the mathematicians far behind. 
Much has been done towards the old duty, ever insistent, of explaining new 
phenomena ; and the names of Maxwell, Weber, Neumann, and Hertz need only to 
be mentioned in order to suggest the progress that has been made in one subject 
alone. We need not hesitate to let our thoughts couple, with the great 
physicists of the century, the leaders of that brilliant band of workers upon the 
properties of matter who carry us on from wonder to wonder with the passage of 
each successive year. 
Further, it has been an age when technical applications have marched at a 
marvellous pace. So great has been their growth that we are apt to forget their 
comparative youth; yet it was only the middle of the century which saw the 
awakening from what now might be regarded as the dark ages. Nor is the field 
of possible application nearing exhaustion: on the contrary, it seems to be in- 
creasing by reason of new discoveries in pure science that yet will find some 
beneficent outcome in practice. Invisible rays and wireless telegraphy may be 
