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formity of the laws of science as derived from fact and hypotheses ; namely, 
the theory of gravitation and the theory of light. Now let us take the theory 
of light. Newton propounded a certain emission theory, and so long as 
that was capable of explaining all the known facts of optical science, 
it was admitted to be a true hypothesis ; but when facts came out 
which could not be made to square with it, did scientific men then 
say — “No; it is treason to go against Newton. Who are you that you 
should dispute with him ? ” On the contrary, scientific men, when 
they got at a new fact, and found that it was likely to lead to a new 
series of facts, welcomed it, and then they obtained — what ? Why, another 
theory, including all the Newtonian theory, together with the new facts 
which could not be made to square with it. The majority of philosophers now 
hold strongly to the undulatory theory ; but, while this contains phenomena 
not in conformity with the Newtonian theory, there are some very awkward 
phenomena which cannot be brought under the undulatory theory, though no 
one has been enabled to devise a new theory differing from both, and yet 
including the new phenomena. Then with regard to gravitation, if some 
discrepancies between that theory and the motions of the planets and 
satellites should be brought to light, they would be admitted to upset that 
theory. The theory has been held loosely by many men of science, and when 
they found a fact that did not square with it, they ignored it. There 
is a feeling among some mathematicians that the theory of gravitation, which 
has hitherto been boasted as the greatest product of the human intellect, will 
have to be abandoned. (Hear, hear.) There is a great discrepancy between 
the calculated elements of the last discovered planet and its observations. 
But the discrepancies discovered in astronomical science have not become 
known to the general public, because there are so few cultivators of pure 
science. There is a great charm about an uncertain science like geology, 
where every man can make some pretty little theory of his own ; and in 
geology it is comparatively easy to make these theories ; but when you 
come to the hard formulas of mathematical science and all the complications 
of differentials, and find it many years before you can understand its hiero- 
glyphics, and know how few men can combine the actual observations of 
the places of planetary and other bodies with those assigned to them by 
science, then it is a very different matter. At Cambridge there are many men 
who can write out for you the lunar and the planetary theories, but how few 
are there of these men who can handle the telescope and measure the positions 
of these bodies. It is, perhaps, no breach of confidence to tell you that even 
so great a philosopher as Babbage has made this admission to me : — “ I am 
inventing (he says) an analytical machine, which the world is not yet ready 
for, and which scientific men are not yet capable of appreciating.” He has 
shown me his working drawings, contained in I do not know how many 
portfolios ; and he says, “ I have made it a condition in my will that these 
things are not to be published until half a century after I am dead and gone, 
because science will not have arrived at a period when my work will be un- 
derstood until half a century has elapsed.” This machine has been devised 
