4, REPORT—1904. 
scientific school centred in the Cavendish laboratory, whose physical spect- 
lations bid fair to render the closing years of the old century and the open- 
ing years of the new as notable as the greatest which have preceded them. 
Now what is the task which these men, and their illustrious fellow- 
labourers out of all lands, have set themselves to accomplish? To what 
end led these ‘new and fruitful physical conceptions’ to which I have 
just referred? It is often described as the discovery of the ‘laws con- 
necting phenomena.’ But this is certainly a misleading, and in my 
opinion a very inadequate, account of the subject. To begin with, it is 
not only inconvenient, but confusing, to describe as ‘ phenomena’ things 
’ which do not appear, which never have appeared, and which never can 
appear, to beings so poorly provided as ourselves with the apparatus of 
sense-perception. But apart from this, which is a linguistic error too 
deeply rooted to be easily exterminated, is it not most inaccurate in sub- 
stance to say that a knowledge of Nature’s laws is all we seek when 
investigating Nature? The physicist looks for something more than 
what, by any stretch of language, can be described as ‘ co-existences’ and 
‘sequences’ between so-called ‘phenomena.’ He seeks for something 
deeper than the laws connecting possible objects of experience. His 
object is physical reality : a reality which may or may not be capable of 
direct perception ; a reality which is in any case independent of it; a 
reality which constitutes the permanent mechanism of that physical 
universe with which our immediate empirical connection is so slight and so 
deceptive. That such a reality exists, though philosophers have doubted, 
is the unalterable faith of science ; and were that faith per impossibile to 
perish under the assaults of critical speculation, science, as men of science 
usually conceive it, would perish likewise. 
If this be so, if one of the tasks of science, and more particularly of 
physics, is to frame a conception of the physical universe in its inner 
reality, then any attempt to compare the different modes in which, at 
different epochs of scientific development, this intellectual picture has 
been drawn, cannot fail to suggest questions of the deepest interest. 
True, I am precluded from dealing with such of these questions as are 
purely philosophical by the character of this occasion ; and with such of 
them as are purely scientific by my own incompetence. But some there 
may be sufliciently near the dividing line to induce the specialists who 
rule by right on either side of it, to view with forgiving eyes any trespasses 
into their legitimate domain which I may be tempted, during the next 
few minutes, to commit. 
Let me then endeavour to compare the outlines of two such pictures, 
of which the first may be taken to represent the views prevalent towards 
the end of the eighteenth century ; a little more than a hundred years 
from the publication of Newton’s‘ Principia,’ and, roughly speaking, about 
midway between that epoch-making date and the present moment. I 
suppose that if at that period the average man of science had been asked 
