11 
as to any extraneous cause of such action, or as to the reasons 
for its being attractive rather than repulsive. Taking advan- 
tage of the defect of knowledge respecting the modus operandi 
of gravity necessarily incident to an early stage of physical 
science, Hume made the gratuitous assertion that in philosophy 
we have nothing to do with causes, but only with laws of 
sequence of phenomena, and that such laws are fixed and 
immutable. This doctrine was maintained, or involved, in 
most of the writings of succeeding metaphysicians, and some 
of those of Germany even sought to prove, by metaphysical 
argument, that “the action at a distance'’'’ is a necessary truth. 
It is not to be wondered at that the prevalence of such views 
should have had the effect of promoting attention to the em- 
pirical part of philosophy, which is concerned only with facts 
and laws, as certified, either directly or by mathematical in- 
ference, by experiment, to the exclusion of theoretical philosophy 
truly so called, which accounts for facts and laws by mathe- 
matical reasoning founded on intelligible hypotheses. This 
tendency of modern empirical philosophy to put aside true and 
ultimate theory is conspicuous in the work above mentioned 
(sec. 15), and seems to have determined in great measure the 
character of its contents. That I have ground for saying this will 
appear from the following quotation taken from the sixth page 
of Lectures on some Recent Advances in Physical Science, 
by Professor P. G. Tait, one of the authors of The Unseen 
Universe. He there asserts that “physical science, in order 
that advances may be made in it, is to be based entirely on 
experiment, or mathematical deductions from experiment. 
There is nothing physical to be learnt a priori. We have no 
right whatever to ascertain a single physical truth without 
seeking for it physically” (meaning, I suppose, experimentally). 
Accordingly in this empirical system, there is entire silence 
respecting the hypotheses which Newton considered to be the 
foundation of all philosophy, and mathematical calculation for 
determining on the principles of hydrodynamics the motions 
and pressure of the ethereal medium, is persistently avoided. 
Yet there is actually no contrariety between these two aspects 
of physical philosophy — the one just as much as the other being 
dependent for its establishment on observation and experiment. 
They are, in fact, related to each other in the same manner as 
are observational astronomy and physical astronomy, the latter 
of which derives its foundation and reality from the other. 
The author of the above passage is clearly not aware that 
empirical philosophy is only a step towards true and ultimate 
philosophy, and that physical science is really advanced, only 
so far as the physical laws discovered and formulated by means 
