1865)

Working on Boole's system, William Stanley Jevons1 (1835-82) Jevons. arrived at a more convenient symbolic method in his works "Pure Logic" (1864), "The Substitution of Similars" (1869), and "The Principles of Science" (1874). The last two of these belong chronologically to our next period, but are mentioned here because they are so closely associated with the preceding logical movement. In "The Principles of Science" Jevons does not deal merely with formal inferences, but goes over the ground traversed by Mill in his inductive logic. Competent critics are of opinion that he displays more knowledge of actual scientific methods of investigation than Mill, but less philosophic insight.

Ferrier.

Among philosophers who cannot be brought definitely within Bailey any school are Samuel Bailey (1791-1870) and James Frederick and Ferrier (1808-64). Bailey, while he is an associationist and a utilitarian, is a realist as regards the external world; holding that perception of objects is an act not capable of resolution into anything else. His realism led him to oppose Berkeley's theory of vision, of which J. S. Mill undertook the defence against him. Ferrier proceeds from the Scottish school, but is an idealist in the manner of Berkeley. In the "Institutes of Metaphysics" (1854) he attempts a strict demonstration of idealism after the geometrical method of Spinoza.

Near the end of our period comes the unfinished Introduction Buckle. to the "History of Civilisation in England," planned out on an immense scale by Henry Thomas Buckle (1821-62). Of this Introduction the first volume appeared in 1857, the second in 1861. It is admittedly the result of a unique range of reading, and displays brilliant generalising powers. The question that has exercised critics is whether the generalisations are of a really scientific kind. Whether accepted or not, many of them have become familiar in current thought, and have had a decidedly stimulating effect.

WHIT

DURING the nineteenth century biology fully kept pace with the THOMAS other sciences in the process of specialisation. In particular, TAKER. much advance was made in botany. The earlier years were Biology. occupied with the introduction of the "natural system variously modified, and the displacement by it of the "artificial

[Best remembered, perhaps, as a political economist.]

[1846

system" of Linnæus. The services of Robert Brown in this respect were referred to in Volume V., p. 754. John Lindley (1799-1865), Sir William Jackson Hooker (1785-1865), and George Bentham, a nephew of Jeremy Bentham, carried forward the movement. Lindley's "Introduction to the Natural System of Botany" appeared in 1830. Sir William Hooker, like Lindley, was the author of an extensive series of works on systematic

JOHN LINDLEY, AFTER J. H. MAGUIRE.
(By permission of the Royal Horticultural Society.)

botany. Several of them deal with mosses and ferns and other cryptogamic plants. In the investigations of cryptogamic botany great progress has been made. This class of investigations is of peculiar importance as a comparative study; for the forms of plants described collectively as "cryptogamic" are extremely various in type, and display a number of transitional structures by which intervals of organisation that at first seemed impassable are bridged over. This is of interest in relation to the doctrine of evolution, the establishment of which is the advance in biological generalisation by which the century is distinguished.

1865)

In connection with the name of Sir William Hooker, his foundation of the herbarium at Kew must be referred to In 1840 he took charge of the Botanical Gardens there. The preparation for his special work was made by botanical

expeditions to Iceland and on the Continent of Europe. His work in geographical botany, as well as the direction of the Botanical Gardens, has been continued by his son, Sir Joseph Dalton Hooker, whose "New Zealand Flora" appeared in 1853. Although botany has reached so high a stage of specialisation, sex in it is only within the present century that such a fundamental point as the distinction of sexes in plants has been completely

Plants.

Zoology.

The

Theory of

[1846

recognised. This distinction had indeed been noted in various cases from a very early period; and the facts had long been beyond doubt for scientific investigators. Yet in the earlier years of the period we are speaking of writers who denied them. could still get serious attention. They have since then been far more elaborately investigated. The embryology of plants, in particular, has been carried some stages further. Of late the subject has entered upon a new phase through its relation to the investigations of Darwin, which must be the principal topic of the present section.

As in botany, so in the other special departments of biology, most names even of the more important writers must be omitted. In zoology, the work of comparative anatomy has been promoted especially by Sir Richard Owen (" Classification of the Mammalia," 1859) and Thomas Henry Huxley ("Man's Place in Nature,” 1863). On questions of general theory these eminent investigators took quite different lines. Towards the great biological revolution of the century Owen appeared mainly as an opponent, while Huxley was its most zealous apostle.

The establishment of the theory of evolution is not only the greatest biological event of our time; it is also the greatest scientific event. As a general biological theory the doctrine of the descent of species from one another can be traced back considerably beyond the beginning of the present period. From about the middle of the eighteenth century biological thinkers had put forward more or less coherent speculations tending in this direction. The speculations of Erasmus Darwin were mentioned in the preceding volume (V., p. 568). On the same line were those of Lamarck in the "Philosophie Zoologique" (1809). In 1844 appeared anonymously "The Vestiges of the Natural History of Creation," now known to have been written by Robert Chambers. The evolutionary ideas of this work attracted attention; but it was not scientifically well-informed, and had little influence on naturalists. The first effective statement of a scientific hypothesis capable of accounting for biological evolution is due to Alfred Russel Wallace and Charles Darwin. To Darwin's work in applying and testing the hypothesis over the whole field of biology is due its final acceptance.

From the Darwinian theory of the causes of evolution it is necessary to distinguish the doctrine of evolution itself. Though

1865]

the doctrine is older, it is only in our own time that the term evolution has come to be used as the antithesis to creation. Evolution is now equivalent in biology to "transmutation of species," and

(By permission, from the painting by the Hon. J. Collier at the National Portrait Gallery.)

is opposed to "special creation" of each kind of organism. In philosophy it is opposed to the doctrine that makes an original act of creation the absolute beginning of things. The philosophic doctrine of evolution takes in as particular cases biological