orical criticism had to a great
extent neutralised the effect of Archbishop Usher's chronology, the
mathematicians and physicists, assuming certain sources of heat in the
earth and sun could have been the only possible ones, tried to set a
limit to the time at the disposal of the geologist and biologist.
Happily the discovery of radio-activity and the new sources of heat
opened up by that discovery, have removed those objections, which were
like a nightmare to both Geology and Biology.

Lyell used to relate the story of a man, who, from a condition of dire
poverty, suddenly became the possessor of vast wealth, and when
remonstrated with by friends on the inadequacy of a subscription he had
offered, the poor fellow exclaimed sadly, 'Ah! you don't know how hard
it is to get the chill of poverty out of one's bones.'

Geologists and biologists alike have long been the victims of this
'chill of poverty,' with respect to past time. So long as physicists
insisted that one hundred millions, or forty millions, or even ten
millions of years, must be the limit of geological time, it was not
possible to avoid the conclusion stated by Lord Salisbury in 1894, 'Of
course, if the mathematicians are right the biologists cannot have what
they demand[150].' But now geologists and biologists may alike feel
that the liberty with respect to _space_, which is granted ungrudgingly
to the astronomer, is no longer withheld from them in regard to _time_.
We can say with old Lamarck:--

'For Nature, Time is nothing. It is never a difficulty, she
always has it at her disposal; and it is for her the means by
which she has accomplished the greatest as well as the least
results. For all the evolution of the earth and of living
beings, Nature needs but three elements--Space, Time and
Matter[151].'

Darwin, equally with Lyell, has suffered from a reaction following on
extravagant and uninformed praise of his work. The fields in which he
laboured single-handed, have yielded to hundreds of workers in many
lands an abundant harvest. New doctrines and improved methods of enquiry
have arisen--Mutationism, Mendelism, Weismannism, Neo-Lamarckism,
Biometrics, Eugenics and what not--are being diligently exploited. But
all of these vigorous growths have their real roots in Darwinism. If we
study Darwin's correspondence, and the successive essays in which he
embodied his views at different periods, we shall find, variation by
mutation