ASTRONOMICAL PHENOMENA AND PROGRESS. 



by Argelander as of 9.5 mag. In Wollaston's 

 catalogue (1790) an object is noted upon a place 

 which, reduced to 1866, accords with that of 

 the variable. There is also a nebula marked on 

 Gary's globe, which is near the spot occupied 

 by the new star. This nebula is not on Her- 

 schel's catalogue. Sir J. Herschel, on the 9th 

 of June, 1842, marked as visible to the naked 

 eye a star whose place agrees so nearly with 

 that assigned to the new variable, that he can- 

 not help believing it to be the same. 



These splendid phenomena have occurred so 

 rarely since the time when scientific apparatus 

 and methods were introduced into astronomical 

 observation, that but little is known of them. 

 The spectrum analysis, this year, has probably 

 thrown more light upon the mystery than all 

 previous investigations. 



Eccentricity of the Earth's Orbit, and its Re- 

 lations to Glacial Epochs. Mr. James Croll has 

 elaborated an ingenious theory in explanation 

 of the glacial epoch, evidences of which abound 

 on the earth's surface. The theory was origi- 

 nally propounded by Sir John Herschel more 

 than 30 years ago, and may briefly be stated 

 as follows: The mean distance of the earth 

 from the sun being nearly invariable, it would 

 at first be supposed that the mean annual sup- 

 ply of light and heat would also be invariable. 

 Calculations show, however, that this mean 

 annual supply would be inversely proportional 

 to the minor axes of the orbit. This would 

 give less heat when the eccentricity of the 

 earth's orbit is approaching toward, or is at 

 its minimum. Mr. Croll offers reasons for be- 

 lieving that the climate, at least in the circurn- 

 polar and temperate zones, would depend on 

 whether the winter of a given region occurred 

 when the earth, at its period of greatest eccen- 

 tricity, was in aphelion or perihelion. If in its 

 aphelion, then the annual average of tempera- 

 ture would be lower ; if in its perihelion, the 

 annual average of temperature would be higher 

 than when the eccentricity was less, or ap- 

 proached more nearly to a circle. He then 

 calculates the difference in the amount of heat 

 at the period of maximum eccentricity to'be as 

 19 to 26, according as winter would take place 

 when the earth was in its aphelion or perihe- 

 lion. The mean annual heat may be assumed 

 to be the same, whatever the eccentricity of the 

 orbit, and yet if the extremes of heat and cold 

 in winter and summer be greater, a colder cli- 

 mate will prevail ; for there will be more ice 

 accumulated in the cold winters than the hot 

 summers can melt. This result will be produced 

 by the vapor (aided by shelter from the rays 

 of the sun) suspended in consequence of aque- 

 ous evaporation. Hence glacial periods oc- 

 curred, when the orbit of the earth was at its 

 greatest eccentricity, on those parts of the 

 earth's surface where it was winter when the 

 earth was in its aphelion ; carboniferous or hot 

 periods occurred where it was winter when the 

 earth was in its perihelion ; and temperate pe- 

 riods when the eccentricity of the earth's orbit 



was at a minimum. All these gradually slide 

 into each other, producing at long-distant pe- 

 riods alternations of cold and heat, some of 

 which are actually observed in geological rec- 

 ords. 



Mr. Croll has calculated values of the eccen- 

 tricity, and longitudes of the perihelion, at in- 

 tervals of 50,000 years for 1,000,000 years past 

 and 1,000,000 years to come, for the purpose 

 of arriving at some better knowledge of these 

 secular changes of climate, proved to result 

 from eccentricity. He has determined the 

 values at epochs of 50,000 years because the 

 eccentricity changes so slowly that it is not 

 necessary to calculate them at shorter intervals. 

 From these the opinion is deduced that the 

 glacial epoch of the geologists began about 

 240,000 years ago, and extended down to about 

 80,000 years ago ; that the time of the greatest 

 cold was 200,000 to 210,000 years ago ; that the 

 next preceding glacial epoch was about 750,000 

 years ago, still another 950,000 years ago, and 

 that a similar condition of things will take place 

 800,000, 900,000, and 1,000,000 years to come. 



This theory has elicited much discussion and 

 able opposition in the English scientific maga- 

 zines. It is claimed by those who dissent from 

 it that, admitting the accuracy of Mr. Croll'a 

 determination of the values of the eccentricity, 

 such a state of facts alone is not sufficient to 

 account for the glacial epoch known to geolo- 

 gists. 



Sun-Spots. At a meeting of the Royal As- 

 tronomical Society, Mr. Huggins presented 

 the result of his observations of bright " gran- 

 ules" on those parts of the sun which are 

 free from spots. These granules are the 

 same appearances which have been called by 

 other observers "willow-leaves," "rice-grains," 

 " shingle-beach," and " bright nodules," all of 

 which terms convey about the same idea of the 

 phenomenon. The granules are distributed 

 over the whole surface of the sun, excepting 

 those areas which contain spots. When ob- 

 served with powers of only 100 diameters, 

 they present the appearance of rice-grains, 

 but at higher powers, irregular masses may be 

 seen. The granules do not appear to be flat 

 disks, but bodies of considerable thickness. 

 They average about 500 miles in breadth, and 

 500 or 600 miles in length ; some being smaller, 

 and occasionally one appearing of 1,000 or 

 1,200 miles in diameter. On many parts of the 

 sun they lie in groups, the components being 

 separated by small intervals. These groups 

 vary in form, in some places taking the shape 

 of round or oval cloud-like masses, and are else- 

 where long, irregularly formed bands. To these 

 groups, and to the varying brightness of the 

 material between the groups and the granules, 

 is to be attributed the coarse mottling of the 

 sun's surface when observed by low powers. 

 By some theorists they are considered to be re- 

 cently condensed incandescent clouds, and by 

 others as ridges, waves, or hills, on the surface 

 of comparatively large luminous clouds. 



