TEE PROGRESS OF SCIENCE. 



189 



thing like seven years. That these 

 recondite phenomena have been disen- 

 tangled and reduced to precise numer- 

 ical statement is at once conclusive evi- 

 dence of method in the madness of 

 terrestrial motions and of exquisite re- 

 finement in astronomical science. 



The much discussed question of the 

 age of the earth may now be said to 

 have risen from the level of figures of 

 speech to the higher plane of numerical 

 expression. We are not able, and we 

 may never be able, to assign the age of 

 the earth in years, or in thousands of 

 years as our most respected teachers 

 have done in the recent past; but we 

 may say without fear of anything 

 worse than literary contradiction that 

 the age of the earth must be reckoned 

 in millions of years. Probably some 

 hundreds of millions of years have 

 elapsed since the earth became habit- 

 able to organic forms. Nature has 

 plenty of time for her operations; and 

 old as the earth must be in comparison 

 with the centuries of human affairs, it 

 is still active with the energy mani- 

 fested in the earliest geological times. 

 The processes of erosion and sedimenta- 

 tion, and that of secular contraction 

 from loss of internal heat, are still 

 asserting themselves occasionally (fre- 

 quently, if a million years be used as 

 the time unit) by such appalling out- 

 bursts as that which has just over- 

 whelmed St. Pierre. And these proc- 

 esses, though fraught with calamities 

 here and there to our race, must go on 

 for millions of years yet to come. 



BIOGRAPHIES OF EMINENT 



CHEMISTS. 

 Within the last few years several 

 particularly attractive biographies of 

 distinguished chemists have been issued 

 as volumes of the 'Century Science 

 Series,' edited by Sir Henry E. Roscoe; 

 they differ from other works in the 

 same line in that they portray the men 

 and their careers more graphically and 

 concisely, and embody at the same time 

 the results of the latest researches. 



One of these, written by Roscoe himself, 

 bears the title 'John Dalton and the 

 rise of Modern Chemistry' (New York, 

 1895). 



Half a dozen memoirs of the Founder 

 of the Atomic Theory had previously 

 appeared, the most noteworthy being 

 those by W. C. Henry (1854), by R. 

 Angus Smith (1856), and by H. Lons- 

 dale (1874). The first named forms 

 one of the volumes printed for the 

 Cavendish Society, the second includes 

 a History of the Atomic Theory from 

 the days of the Greeks to the time of 

 Dalton, and is embellished with the 

 most satisfactory of the printed por- 

 traits. 



Roscoe's charming work is enlivened 

 with facsimiles, extracts from letters, 

 papers and books by Dalton, reminis- 

 cences by contemporaries, appreciations 

 by later chemists and amusing anec- 

 dotes, the whole so simply and yet so 

 vigorously written as to make a delight- 

 ful narrative. There has always been 

 much speculation as to the mental proc- 

 esses which led Dalton to conceive of 

 the great theory indissolubly connected 

 with his name, and this problem has 

 only been quite recently solved by the 

 discovery in the rooms of the Literary 

 and Philosophical Society of Manches- 

 ter (where the whole of the experi- 

 mental work was carried on by Dalton) 

 of his laboratory and lecture notebooks, 

 in a number of volumes. It has been 

 supposed that it was the experimental 

 discovery of the law of combination in 

 multiple proportions that led Dalton 

 to the idea that chemical combination 

 consists in the approximation of atoms 

 of definite and characteristic weight, 

 the atomic theory being thus adopted 

 to explain the facts ascertained by 

 chemical analysis. But an examina- 

 tion of these newly discovered manu- 

 script notes shows that he arrived at 

 these ideas from purely physical con- 

 siderations along the line of the New- 

 tonian doctrine of the atomic consti- 

 tution of matter; he conceived of 

 chemical combination as taking place 



