290 ANNUAL OF SCIENTIFIC DISCOVERY. 



of heat causing a mass of liquid to assume a gaseous form, and 

 vice versa. So that the heat withdrawn by Jupiter and Venus 

 from the side exposed toward them might be sufficient to cause a 

 copious condensation of gases, which might have a visible effect 

 directly, or produce mechanical changes by means of altered re- 

 flection varying the distribution of a great amount of heat. 



Mr. Balfour Stewart, in a lecture before the Royal Institution, 

 London, on the sun as a variable star, expressed the opinion that 

 the spots on the sun's surface are produced by downward currents 

 of the surrounding atmosphere, the depth of which had been esti- 

 mated at not less than 72,000 miles. A downward-rush of atmos- 

 phere occasioned an exposure of the body of the sun, and pro- 

 duced an appearance of a dark spot; an upward rush of the at- 

 mosphere produced the bright faculse that surround the dark 

 spots, and are seen more conspicuously on the borders of the sun's 

 disc. This atmosphere, he thought, was very sensitive to the 

 approach of the planets, especially of Venus, in consequence of 

 its comparatively short distance, and of Jupiter, in consequence 

 of its size. When Venus is opposite to the earth, the spots attain 

 their maximum, which is sometimes as much as 15,000 miles in 

 diameter. From these spots we estimate that the sun rotates on 

 its axis once in about 25 days ; but there is reason to believe that 

 the spots rotate faster than the body of the sun, owing to the more 

 rapid rotation of the upper portions of the atmosphere, which, on 

 being carried nearer to the centre by a downward current, retains 

 the velocity it before possessed, in the same manner as the trade 

 winds on the earth are supposed to be caused by the different 

 velocities of the air near the poles and in the equatorial regions. 

 In addition to the influencing causes attributable to the move- 

 ments of the planets, there are periodical variations of the spots 

 occurring about every 10 years, which cannot thus be accounted 

 for. The lecturer spoke of the corona observed during the last 

 total eclipse of the sun, which he attributed to its atmosphere, and 

 it was on calculations founded on those appearances that the 

 height of the sun's atmosphere had been conjectured. 



M. Hock, taking the mass of a planet and the inverse cube of 

 its distance as the measure of the planet's influence in raising 

 waves of disturbance on the sun, assigns to Mercury, Venus, the 

 Earth, Mars, Jupiter, and Saturn, effects proportional to the num- 

 bers 12, 24, 10, 0, 23, and 7, respectively. 



According to M. Faye, the interior of the sun is a " nebulous, 

 gaseous mass, of feeble radiating power at a temperature of dis- 

 sociation," a sun spot being caused by the heating effects of an 

 "up-rush" from the interior breaking through the less intensely 

 boated photosphere. English observers refer the sun spots to the 

 cooling effects of a " down-rush " from the exterior. Mr. J. N. 

 Lockyer's spectroscopic observations confirm the latter view. In 

 the spectrum of light from the spot the absorption bands were 

 visible, as in the spectrum given by the photosphere, and appar- 

 ently even thicker ; further, no bright lines were visible. This, if 

 confirmed by the observation of larger spots, would establish the 

 presence of deycending currents, without deciding the question of 



