ASTRONOMICAL PHENOMENA AND PROGRESS. 



45 



prove the reality of these variations in the solar 

 diameter. 



From an examination of the curves of these 

 variations, Secchi deduced that the diameter 

 had minima values when the numbers of spots 

 and protuberances were at the maxima. This 

 result shows that there is a physical relation 

 which merits a special study. The region be- 

 tween 20 and 23 degrees of heliographic lati- 

 tudes iiiiorls the smallest diameters, and this 

 is exactly the zone where the solar activity is 

 tlie greatest, as resulted trom the comparisons 

 and extent of the protuberances and spots. 

 Secchi thus provisionally accounts for the 

 above relation. The border of the sun is not 

 perfectly defined, the want of definition in its 

 contour being, probably, due to the light of 

 the chromosphere, which, very bright at its 

 base, fuses to some extent with the photo- 

 sphere. The ordinary diameter of the sun is 

 composed of the diameter of the photosphere 

 augmented by this brighter inferior layer, 

 whose height equals 4 seconds, which his meas- 

 nrers assign as the difference between the 

 semi-diameter observed and that of the ephem- 

 eridis. If this explanation be true, knowing 

 that the chromosphere is sometimes more and 

 sometimes less brilliant, it results that the so- 

 lar diameter, thus augmented, will he found 

 to diminish and to increase with the brilliancy 

 of the chromosphere. 



Sparer'* Obtercationt on the Sun. Prof. 

 Sporer has contributed to the Berlin Academy 

 of Science full reports of his recent observa- 

 tions on the sun. He gives interesting com- 

 parisons of spots, showing the difference be- 

 tween the two hemispheres of the sun in re- 

 spect to the frequency of spots, and the mean 

 heliographic latitudes. As to the frequency 

 of spots, it appears that the southern hemi- 

 sphere exceeds the northern both in maximum 

 nnd minimum. The curves also show dis- 

 tinctly the rapid passage from minimum to 

 maximum, and the slow decrease of the maxi- 

 mum. 



The mean heliographic latitudes are ob- 

 tained through assigning to ench group of spots 

 a factor of value. The union of five-rotation 

 periods gave a point of the curve for the north- 

 ern as well as for the southern hemisphere. 

 Carrington had obtained from his observations 

 the striking result, that the spots at the time 

 of the minimum approach the equator, there- 

 after veered off to higher latitudes, and that 

 then the more numerously spotted zones grad- 

 ually approach the equator. Spflrer, hy his 

 observations since 1861, has confirmed this 

 result. 



Spflrer adheres to his division of protuber- 

 ances into two classes. Secchi, in his work on 

 the sun, has distinguished four classes of pro- 

 tnbemnces, hut afterward accepted Sporer's 

 twofold division. Both observers are at one 

 in this that the protuberances, which Sp6rer 

 has named "flame" and Secchi "ray" protn- 

 terances, give different spectral lines, and 



stand in intimate connection with the spots. 

 But with regard to the proper hydrogen pro- 

 tuberances, Secchi says they are not in the 

 condition to give rise to a spot, against which 

 Sporer adduces examples of their influence in 

 neighboring spot-formation, especially promi- 

 nent in the intervals between considerable 

 protuberances of hydrogen. 



Solar Otoercationt made easy. Mr. R. Lang- 

 don describes in Nature his successful at- 

 tempts to see the red flames on the-sun's limb 

 without waiting for a total solar eclipse, and 

 by the use of a common telescope. He says : 



I cut out several circular disks of thin brass 

 ^blackened on both sides), leaving three arms pro- 

 jecting from the periphery of each, of such length 

 that when the ends were bent they should slide into 

 the tube of the eye-piece, I placed one such disk 

 in the eye-tube as near to the field lens as possible 

 to avoid its getting hot ; but here a difficulty pre- 

 sented itself which I had not foreseen the disk was 

 a trifle too large, and it shut out the sun altogether. 

 I put in a smaller one which admitted too much of 

 the sun's light. I afterward tried several, and it re- 

 quired a considerable amount of filing and scraping 

 to produce one just the right size to cover the sun's 

 disk and no more ; especially as the least jarring or 

 vibration of the telescope would cause the edge of 

 the sun to be seen first on one side and then on the 

 other. Alter several trials at different times I suc- 

 ceeded on January 16, 1872, in seeing on the south- 

 western limb a red flame. It appeared rather wider 

 at the top than the bottom, with a smaller one grow- 

 ing out from the bottom or root close to the sun's 

 limb. There was another tongue of flame a little to 

 the right, which appeared toT>e detached from the 

 larger flame and also from the sun's limb. 



On September 20 ? 1872, I saw a red flame which 

 went up a little distance from the sun's limb and 

 then divided in three. Close to this, on the edge 

 of the sun's disk, was a group of nine small spots, 

 and a large space was covered with t'neulie. The 

 flame which was of a deep-red color did not ap- 

 pear to be projected against the sky, but upon a very 

 delicate purple background. 



No colored glass was used in either of these ob- 

 servations, but a sheet of letter-paper was held be- 

 tween the eye and the telescope, winch was removed 

 the instant the sun was brought into the centre of 

 the field of view. 



The Zodiatal Light. Mr. Maxwell Hall 

 describes in Nature the appearance of the 

 zodiacal light, as seen in November, 1872, 

 from Jamaica. The light reached a point 

 between the Pleiades and the Hyades, so that 

 the central portion traced ont the course of 

 the ecliptic with wonderful precision ; it was 

 brightest in the central part of the hand, and 

 gradually faded off toward the edges; its 

 illuminative parts were greater than that of 

 the Milky-Way, but became fainter as it pro- 

 ceeded along the ecliptic ; as late as midnight 

 a faint glare could be seen above the horizon. 

 The breadth of the light was 40 at a distance 

 of 34* from the sun, and 10 at a distance of 

 139 from the ran, and the light faded out at 

 the distance of about 177 from the sun. It 

 seemed perfectly fixed in the horizon, and 

 there was no sign of its displacement such as 

 might be caused by parallax combined with 

 the earth's rotation, and, where the brighter 

 part had set, and was far below the horizon, 



