VI 
PREFACE. 
truth. And in connection with this remark allusion may 
here be made to one or two of the many recent researches in 
Physical Scieuce. In a work just published,* Professor 
P. G. Tait speaks of “the Law of the Dissipation of Energy, 
discovered by Sir W. Thomson/* and adds that it has 
already led to an important discovery which refutes the 
Uniformitarian theories of geologists : 
“ It enables us distinctly to say, that the present order of things has not 
been evolved through infinite past time by the agency of laws now at work, 
but must have had a distinct beginning — a state beyond which we are 
totally unable to penetrate, a state which must have been produced by 
other than the now (visibly) acting causes.” 
And, arguing from our present knowledge of radiation, 
against the claims of 
“ Lyell and others, especially of Darwin, who tell us that even for a com- 
paratively brief portion of recent geological history three hundred millions 
of years will not suffice,” 
Professor Tait quotes Sir W. Thompson’s three lines of 
argument, and urges 
“ Ten million years as the utmost we can give to geologists for their 
speculations as to the history even of the lowest orders of fossils [and] for 
all the changes that have taken place on the earth’s surface since vegetable 
life of the lowest known form was capable of existing there.” 
Of course, it remains to be seen how far future researches 
may induce others to modify the above statements. An 
example of the change in our conceptions of Nature resulting 
from recent investigations, is afforded by the fact that whilst 
the use of improved telescopes was considered to have resolved 
some of the nebulae into multitudes of stars, spectrum analysis 
now shows them to be, wholly or in part, masses of glowing 
or incandescent gas. These remarks can scarcely be concluded 
without a reference to the researches into what Professor 
* Recent Researches in Physical Science. 2nd Edition, 1870 
