ASTRONOMICAL I'llKNoMENA AND PROGRESS. 



69 



had boon SO much colder 



in question tlian at present, the 



ii the other hand, ought to have 



ir, owing to the sun's irreat- 



\VelV the Sllll's (listftnCO till l.V 



ut that det'-rniincd tlie temperature, the 



;i ..ulil h:i\ e lieen, (it least, 45 warmer 



than the present, a-; surely as the winters \vere 



IdiT than the present, at the superior 

 limit of tlu eccentricity 850,000 years ago. Had 

 there could have been no 

 L'lacial epoch ; for :i summer so warm, not- 

 with-tanding its shortness, would have been 

 suiHcient to iue.lt the snows of winter. In that 



tin- theory \vhich attributes the glacial 



epoch to an extreme condition of eccentricity 



would have in be abandoned. The purely as- 



ts of eccentricity, as has been 



> shown by Sir John Herschcl, Arago, 

 Huinboldt, and others, are compensated by 

 others of an opposite character, so that eccen- 

 tricity, viewed from an astronomical stand-point, 



not appear capable of accounting (the 

 author admits) for the glacial epoch. But he 

 claims that the astronomical effect is far more 

 than neutralized by causes of a physical nature. 

 One of these causes is the presence of snow 

 and \'".\ during which dense fogs prevail and 

 cut off a great portion of the sun's rays, and thus 

 D the summer temperature. Even supposing 

 the sun's rays were to reach the earth with 



full intensity, they would no doubt melt 

 DW accumulated during the long winter; 

 but they would fail to raise the summer tem- 

 perature as long as the snow remained un- 

 invited. The air is cooled by radiation from 

 snow and ice more rapidly than it is heated by 



;n; and, as a consequence, in a country 



reenlaod, covered with an icy mantle, the 

 temperature of the air, even during summer, 

 seldom rises above the freezing point. Were it 

 >: the iee. the summers of north Greenland, 

 owing to the continuance of the sun above the 

 horizon, would be as warm as those of England ; 

 hut instead of this, the Greenland summers are 

 colder than the English winters. If India were 



d with an ice-sheet, its summers would 

 be colder than those of England. If at a glacial 

 epoch the heat of the sun, during the short 

 summer in particular, failed to melt the total 

 quantity of snow accumulated during the long 

 and intensely cold winter, then the snow and 

 ice would accumulate year after year, till the 

 of the entire country was covered. Af- 

 :is the mean temperature of the summers, 

 no matter what might be the intensity of the 

 MIII'S rays, could not rise far above the freezing 

 point. At those periods of extreme eccentri- 

 city, when the winter occurred in perihelion, 



would he a short and warm winter and 



a long and moderately cold summer. The mid- 



Miinme'- temperature 850,000 years ago, did the 



winter occur in perihelion, 'would be about 



determined according to the sun's dis- 



At the periods 950,000 and 750,000 



ago, the temperature would be 39 and 



86 respectively. But again, there are but few 

 modifying can-is which would prevent thepOB- 

 sihility of the summer temperature ever fulling 

 BO low as 27 or oven 86; for, siirrouii'i 

 a warm sea, the summers could at that time no 

 more have been cold than during the glacial 

 epoch they could have been warm, when the 

 land was covered with ice. Mr. Croll concludes 

 his paper with an inquiry into the probable 

 amount of heat conveyed by the Gulf Stream 

 from the tropics, to the temperate and arctic 

 regions, at different periods of the remote past. 

 Researches on Solar Physics. Warren de la 

 Rue; Baltbur Stewart, superintendent of 

 the Kew Observatory; and Benjamin Lowry, 

 observer and computer to the Kew Obser- 

 vatory, have published, for private circula- 

 tion, a memoir with the above name, in 

 which they give the history of their observations 

 upon sun-spots. The following are the more 

 important conclusions at which they have ar- 

 rived: 1. The umbra of a spot is nearer the 

 sun's centre than its penumbra, or, in other 

 words, it is at a lower level ; 2. Solar faculae, 

 and probably also the whole photosphere, con- 

 sist of solid and liquid bodies of greater or less 

 magnitude, either slowly sinking or suspended 

 in equilibria in a gaseous medium ; 3. A spot 

 including both umbra and penumbra is a phe- 

 nomenon which takes place beneath the level of 

 the sun's photosphere. These gentlemen, in a 

 communication to the Koyal Society, mention 

 that Hofrath Schwabe has called their atten- 

 tion to certain phenomena on the surface of 

 the sun which he had noticed on two occa- 

 sions when there was a minimum in the num- 

 ber of sun-spots. These phenomena were: 

 1. A total absence of facula) and faculous mat- 

 ter : 2. Absence of the usually-observed scars, 

 pores, and similar appearances ; 3. An equal 

 brightness of the whole surface, the limb being 

 as luminous as the centre. Mr. Schwabe also 

 remarks that he has noticed a connection be- 

 tween sun-spots and meteoric showers. He 

 finds that the minimum of spot-frequency coin- 

 cides remarkably with the recurrence of the 

 meteoric showers, the period of rotation of 

 which agrees with a larger period of the sun- 

 spots. In 1833 there was an extreme scarcity 

 of spots (only thirty-three small groups being 

 observed) and in 1866 and 1867, after thirty- 

 three years, the phenomenon repeats itself. 

 From January 1 to June 8, 1867, he had ob- 

 served only six small groups, and, out of one 

 hundred and thirty-three days of observation, 

 there were one hundred without spots. 



The authors subsequently announced, in the 

 monthly notices of the Royal Society, that they 

 had specially investigated the relation between 

 solar activity and t!ie ecliptical longitude of 

 the planets, and, as a result, they believe that 

 they have discovered a connection between the 

 behavior of sun-spots and the longitudes of 

 Venus and Jupiter. By a comparison of Car- 

 rington's diagrams exhibiting the distribution 

 in heliographic latitude of sun-spots from thne 



