3 i4 POPULAR SCIENCE MONTHLY. 



died in 1875 at the age of seventy-eight. The most important por- 

 tions of Lyell's work were done after he had passed forty years ; com- 

 plete and sweeping revisions and enlargements of his earlier work 

 were done late in life, and even down to within three days before his 

 death, at the age of seventy-eight years, he finished a revision of his 

 ' Principles of Geology/ a work which amazed and electrified scientists 

 of all nations, and remains to-day the unchallenged great text-book 

 in that field. Lyell's is the broadest and best-balanced mind which 

 has dealt with deep-lying geological problems. In effect, he may be 

 said to have created the science of geology. His work marked the 

 second epoch in the thought of mankind, supplying the needed second 

 link in the chain of evidence of planetary evolution. He applied in 

 geology the principle of gradual development to the earth's crust, 

 which Laplace and Kant had previously wrought in astronomy con- 

 cerning sun systems and planets; which Darwin accomplished after- 

 ward in biology for living forms and organic life, and Spencer achieved 

 for psychology in human consciousness and thought, and for sociology 

 in human society and government. And, moreover, the fuller ampli- 

 fication of Lyell's work was made after he had passed sixty years. 



With Lyell's work planetary evolution came to be a recognized 

 and definite truth ; and then came Charles Darwin. Darwin was born 

 in 1809, and lived until the age of seventy-three. His lifelong habits 

 of thought, and his methods of research are too well known to be 

 repeated, but it may be said that up to the age of forty-nine years he 

 devoted himself almost wholly to accumulating stores of experience 

 and observation, and to the planning of the great work which was to 

 come afterward. ' The Origin of Species,' written at the age of 

 fifty, sounded the farthest depth of biological knowledge and created 

 such a whirlwind of controversy as no other book has done. His 

 ' Descent of Man,' written at the age of sixty-two, was not less remark- 

 able, and had an effect almost as widespread and profound. No man 

 then living, either young or old, had the preparation, patience in the 

 working out of details, breadth of mind, modesty or the honest sim- 

 plicity of character, necessary to the carrying out of his tremendous 

 task. Darwin may not have created the science of biology, but unmis- 

 takably he brought it out of a vague, confusing and conflicting state, 

 reduced the mass of evidence and details to concrete form, and made 

 it into an orderly and perfect system. 



Herbert Spencer, the latest of this remarkable group of investiga- 

 tors, died in 1904, at the age of eighty-three. Spencer's mind did not 

 begin its best functions until he was well on into the forties. He was 

 storing up until then — his mind was incubating, as it were. At forty 

 he had made merely a rough outline or program of his ' Synthetic 

 Philosophy,' which massive work he was to carry out triumphantly in 



