8o6 THE POPULAR SCIENCE MONTHLY. 



and the quantity of heat received from the sun by the earth in 

 different parts of its orbit is supposed to be correspondingly modi- 

 fied. These differences are greatest when the eccentricity is 

 greatest. If with this is combined such a position of the equi- 

 noxes that summer in one hemisphere shall correspond with the 

 perihelion and winter with the aphelion, the contrast of the sea- 

 sons in that hemisphere will be most marked, and we shall have 

 the conditions, according to one theory, for a glacial period. 



Such, according to M. Jean Reynaud, was the case in the 

 northern hemisphere about 9500 B. c, when, he thinks, our last 

 glacial period was at its height. From that time the differences 

 were gradually reduced till about 1250 a. d,, when they became 

 least, and the northern seasons were mildest and most equable. 

 The differences then began to enlarge again, and we are now ad- 

 vanced a little more than six hundred years toward another gla- 

 cial period. According to this theory, the seasons were growing 

 milder all through human history till 1250 A. D,, and have been 

 tending to become more severe since then. 



A question of fact is here presented, evidence respecting which 

 is sought, in the absence of exact observations, in such records as 

 may happen to exist of the character of seasons in the j^ast. M. 

 Arago several years ago collected a considerable list of mentions 

 in the literature and documents of former times of periods of un- 

 usual cold, of long or cold winters, unusually hard freezing of 

 rivers, and remarkable heat, drought, or rain, which constitutes 

 our principal source of information on the subject. Parts of this 

 list have been used by M. Jules Peroche and M. Amad^e Guille- 

 min to establish opposite conclusions as to the validity of M. Rey- 

 naud's hypothesis. 



Latin poets furnish some of these data, as when Ovid com- 

 plains of the inclemency of his place of exile on the Black Sea, in 

 what is now pleasant southern Russia ; or Horace and his com- 

 peers describe terrible storms in Rome; or Juvenal tells of a 

 Roman lady having to break the ice of the Tiber to wash her 

 face. Cicero and some of the historians speak of the severe cli- 

 mates of Gaul and other outlying provinces, evidently contrast- 

 ing them with the pleasures of life in Italy. The discomforts ex- 

 perienced by Hannibal in crossing the Alps were what an army 

 from the south would suffer in any age in crossing those mountains 

 in winter, if they were roadless and inhabited by barbarians. To 

 a candid critic, these representations mean nothing on one side or 

 the other, and such is the conclusion which M. Angot has reached 

 after carefully examining the subject. 



Of fifty-six instances of extreme winter severity cited by M. 

 Peroche from M. Arago's list, fourteen occurred before the sup- 

 posed "Great Summer" year, 1250. There seem to be more of 



