Notices respecting New Boohs. 465 



a problem which previous to that time had engaged and perplexed 

 many minds. Till Dr. Croll's famous theory appeared in the pages 

 of this Magazine, no hypothesis had been propounded which satisfied 

 the conditions of the problem even as known at the time ; while 

 the various tentative explanations for the most part demanded the 

 calling into existence of agencies and of terrestrial changes which 

 would themselves be more difficult to account for than the phe- 

 nomena they were meant to explain. It was from the first seen 

 and conceded that the varying eccentricity of the ecliptic, upon 

 which Dr. Croll bases his theory, has a real existence in nature ; 

 and the only points then, and now, in dispute have relation to the 

 manner and extent to which these cosmical causes affect terrestrial 

 chmate and conditions. Early in the century, Sir John Herschel, 

 Arago, and others had given attention to the question of the rela- 

 tion of eccentricity to climate ; and they came to the conclusion 

 that it neither affects the amount of heat received from the earth 

 nor, to any appreciable extent, its distribution. 



Dr. Croll thus brought out his theory in the face of, and against, 

 the confidently expressed opinion of some of the greatest authorities 

 in physical science. The door which he sought to open had been 

 officially barred for a long generation, and when he pushed through 

 it he found no beaten path on the other side. Notwithstanding all 

 that had been written about the Glacial Epoch, the facts and phe- 

 nomena of the period were but imperfectly stated and understood, 

 and the science of Climatology was either non-existent or in the 

 most chaotic condition. Gradually and laboriously he built up his 

 theory ; he accumulated facts and observations with the most pains- 

 taking industry ; and these he marshalled and arranged with con- 

 summate skill, till he built up and solidly buttressed one of the 

 most important and far-reaching doctrines which has been enun- 

 ciated in the whole range of geological science. In dealing with 

 the climatological and other physical facts and bearings of his sub- 

 ject, Dr. Croll had little help from the investigations of those who 

 had gone before him. He had, indeed, to combat many erroneous 

 notions which had become generally entertained from the works of 

 popular writers. Of the great physicists, some had given opinions 

 directly opposed to Dr. Croll's contentions ; others had given no 

 consideration to the climatological relations of terrestrial and cos- 

 mical phenomena ; and many were by no means agreed as to the 

 effects of such phenomena. Thus there was scarcely any ready- 

 made help available for incorporation with Dr. Croll's work ; he 

 had few witnesses to call in his favour ; he had many stumbling- 

 blocks to remove, much to explain away, and much to argue against. 

 With indomitable patience and perseverance he set himself to his 

 task ; with calmness and temperance, and yet with marvellous in- 

 tellectual alertness, he met the arguments of opponents, adhering 

 to his position, and maintaining his view, with modest tenacity and 

 resolution, which commanded the respect and esteem of his most 

 powerful opponents. 



The greater part of what Dr. Croll has written on the subject of 



