July 12, 1895.] 



SCIENCE. 



83 



laws of their appearance may be finally 

 determined, and their connection with the 

 formation of spots and prominences satis- 

 factorily made out. Similar results from 

 the work of M. Deslandres, of the Pai-is 

 Observatorj', are given in Mr. Maunder's 

 paper in Knoidedge, for January, 1896. 



Both spots and prominences have a well 

 recognized variation in heliographic or solar 

 latitude ; the former has been investigated 

 by Dr. Spoerer of Potsdam, and the latter 

 by M. Ricco of Palermo. Just before the 

 epoch of a minimum (1888, for example) 

 the spots are seen nearest the Sun's equa- 

 tor ; coincidently with the minimum these 

 circum-equatorial spots cease, and a series 

 breaks out afresh in high solar latitudes. 

 Thenceforward to the time of the next mini- 

 mum the mean latitude of the spots tends 

 to decline continuously. This fluctuation 

 is called 'the law of zones.' Dr. Spoerer 's 

 investigations further show an occasional 

 predominence of spots in the Sun's southern 

 hemisphere not counterbalanced by a corre- 

 sponding appearance in the northern. Al- 

 so, during the last half of the seventeenth 

 century and the early years of the eigh- 

 teenth, there seems to have been a remark- 

 able interruption of the ordinary course of 

 the spot cycle, and the law of zones, too, 

 was apparently in abeyance. The latitude 

 variations of the prominences follow quite 

 closely the fluctuations of the spots, al- 

 though exhibiting a greater divergence be- 

 tween the Sun's two hemispheres than the 

 spots do. 



Independently of his light and heat, the 

 Sun's supreme right to rule his familj^ of 

 planets is at once apparent from his su- 

 perior size, and from his vastly greater mass. 

 Eelative weights of common things readily 

 give a notion sufficiently precise: let the 

 ordinary bronze cent represent the weight 

 of the Earth; Mercury and Mars, then, the 

 smallest planets, would, if merged in one, 

 equal an old-fashioned silver three-cent 



piece; Venus, a silver dime; Uranus, a gold 

 double-eagle and a silver half-dollar (or, 

 what is about the same thing in weight, a 

 silver dollar, half dollar, and a quarter dol- 

 lar taken together); ISTeptune, two silver 

 dollars; Saturn, eleven silver dollars; Ju- 

 piter, rather more than two pounds avoir- 

 dupois (37 silver dollars); while the sun, 

 outweighing 750 times all the planets taken 

 together, would somewhat exceed the weight 

 of the long ton. 



As the Sun shines with inconceivably 

 greater power than any terrestrial source, 

 an idea of its total light is difficult to convey 

 intelligibly in terms of the ordinary stand- 

 ards adopted by phj^sicists. Its intrinsic 

 brightness, or amount of light per square 

 unit of luminoiis surface, exceeds the glow- 

 ing carbon of the electric arc light about Be- 

 times, or the glowing lime of the calcium 

 light about 150 times. " Even the darkest 

 part of a sun-spot outshines the lime light " 

 (Young). Some rude notion of the total 

 quantity of light received from the Sun is 

 perhaps obtainable on comparison with the 

 average full moon, whose radiance the Sun 

 exceeds 600,000 times. In consequence of 

 absorption of the Sun's light bj^ its own at- 

 mosphere, the Earth receives very much 

 less than it otherwise would; while if the 

 absorbing property of the atmosphere were 

 entirely removed, the Sun would (accord- 

 ing to Professor Langlej') shine two or three 

 times brighter, with a color decidedly blue, 

 resembling the electric arc. As a further 

 effect of this absorj)tion, the intrinsic bright- 

 ness at the edge is § that of the centre of 

 the disk (according to Professor Pickering); 

 and Dr. Vogel makes the actinic or photo- 

 graphic intensity only i for the same re- 

 gion. While this shading olf towards the 

 edge is at once apparent to the eye, when 

 the entire Sun is projected on a screen, the 

 rapid actinic gradation is more marked in 

 photographs of the Sun, which strongly 

 show the effect of under-exposure near the 



