Dr. Croll's Theory of Glacial and Warm Periods. 6$ 



A Criticism of Dr. Croll's Theory of Alternate Glacial 

 and Warm Periods in each Hemisphere, and of 

 Interglacial Climates. By Henry H. Howorth, 

 M.P., F.S.A. 



{Received December jist, i88p.)- 



I propose in the following pages to criticise a theory 

 which dominates a large number of scientific men and is the 

 foster-mother of much additional speculation, I mean Dr. 

 Croll's famous explanation of geological changes of climate 

 which he elaborated in a series of papers in the PJiilo- 

 sophical Magazine, and afterwards stated more fully in his 

 well-known works " Climate and Time and " Climate and 

 Cosmology." Not only is this theory widely held, but it 

 would be difficult to find one supported by greater skill and 

 ingenuity, nor are there many works better worth reading 

 and more inspiring than the two just named. I wish to 

 say this the more emphatically because I cannot accept 

 their conclusions. 



There is nothing hesitating or apologetic about Dr. Croll's 

 attitude. " I have studiously avoided," he says, " introduc- 

 ing anything of a hypothetical character. All the conclu- 

 sions are based either on known facts, or admitted physical 

 principles. In short, the aim of the work is to prove that 

 similar changes of climate follow, as a necessary effect, from 

 admitted physical agencies, and that these changes, in as 

 far as the past climatic condition of the globe is concerned, 

 fully meet the demand of the geologist." (Preface V. and VI.) 



It is not quite easy to concentrate the essential elements 

 of Dr. Croll's argument since his work contains several long- 

 parenthetical chapters discussing side issues. I will try to 

 E 



