INVESTIGATION OF TEMPERATURE CHANGES. 241 



After due consideration of the facts here presented it seems not unreason- 

 able to make the assertion that, on the whole, there is evidence, very 

 considerable in amount and importance, to the effect that a decrease of 

 temperature during historic times has manifested itself in various ways be- 

 sides desiccation ; and that if such decrease has not yet become perceptible 

 in instrumental records, it is because the conditions under which observa- 

 tions have been taken are not satisfactory, and the length of time they have 

 been kept up is not suflicient for the demonstration of a change, which, 

 although perhaps properly called rapid when looked at from the geological 

 point of view, is very slow as compared with the ordinary progress of his- 

 torical events. If the facts which have been given in the preceding pages 

 were not supported by others of a similar kind, or if they were contradicted by 

 more definitely ascertained occurrences of an opposite character, it might be 

 justifiable to look upon them with suspicion, and as possibly to be explained 

 in some other way than by admitting an actual cooling of more or less of the 

 earth's surface. When, however, we consider that we have been led directly 

 to the hypothesis of decreased temperature by a long array of facts which 

 seemed to demand the intervention of that agency, our reluctance to accept 

 the indicated deterioration of climate cannot but be lessened. Much more 

 ought this to be the case, if in going back into prehistoric times we find that 

 geology furnishes us with evidence of a similar character ; and when we do 

 inquire of that science whether proof can be furnished from its records that 

 the temperature of the earth's surface has been diminishing during the geo- 

 logical ages, we find the answer so fully and entirely in the affirmative that 

 all hesitation about the validity of the conclusions already reached may be 

 laid aside. c 



It is not intended in the present work to go into anything like an exhaus- 

 tive investigation of the data on which the assertion made in the preceding 

 paragraph is based. Such a course would involve an almost complete review 

 of the whole stock of geological observations, and the use of an unlimited 

 amount of space for displaying them. All that will be attempted will be to 

 cite a few of the best-known fiicts by which we are guided toward the con- 

 clusion that throughout the earth, from epoch to epoch, a decrease of heat 

 has, on the whole, been the rule. 



climate of any region is one as yet quite unfamiliar to the popular mind. So, too, tlie difficulties in the way of 

 believinn' the accounts of the voyages of the Norsemen to our own shores will be decidedly lesseneil by adopting 

 the theory that there has been some deterioration of the climate in this country during the past eight or nine 

 centuries. 



