ASTRONOMICAL PHENOMENA AND PROGRESS. 



35 



eclipse-observations indicated a change in the 

 color and appearance of the corona. The gas- 

 eous elements were much less conspicuous than 

 in the eclipses of 1869, 1870, and 1871, near 

 the epoch of sun-spot maximum. In short, 

 the conclusion of most astronomers is that 

 the non-gaseous matter of the corona is cos- 

 mical, while the gaseous elements so conspicu- 

 ous in eclipses at the epochs of spot maxima 

 are strictly solar, consisting of torrents thrown 

 out to great distances by the sun's eruptive 

 force. "In spot-maximum years," says Mr. 

 Lockyer, '* we have violent up-rushes of gas 

 from the sun's interior, and the corona is main- 

 ly built up of such gas. Further, we have 

 spots, and, if these are not evidences of the re- 

 turn convection currents, we have none other. 

 In spot-minimum years, such as the present, 

 we have no up-rushes, and the corona contains 

 no gas, and there are no spots. Spots, then, 

 are only observed when we have a right to 

 look for the return of the upward current, 

 about which there is no doubt, and the rate of 

 which we have measured." 



The serrations known as Bayly's beads re- 

 mained visible, according to Mr. Colbert, for 

 two and a half seconds, indicating that the 

 mountains around the moon's disk are one and 

 a half mile high. 



The Relation between Sun-spot Frequency 

 and Changes in the Earth's Atmosphere. The 

 "American Journal of Science" for June, 

 1878, contains a letter from Dr. B. A. Gould, 

 Director of the Cordoba (S. A.) Observatory, 

 announcing the probable discovery of a mutual 

 relation between the number of sun-spots and 

 the condition of the earth's atmosphere. Dur- 

 ing the first two or three years of Dr. Gould's 

 residence at Cordoba at the epoch of sun- 

 spot maximum the state of the atmosphere 

 was eminently favorable for astronomical ob- 

 servations. With the change, however, in the 

 condition of the sun's surface, a simultaneous 

 variation occurred in the atmosphere and mean 

 temperature of Buenos Ayres and the Argen- 

 tine Republic. In 1877 there were but ten 

 clear nights at Cordoba during the months of 

 March and April, while in July and August 

 the number was still less; and from January 1 

 to March 20, 1878, there was but one clear 

 night. In Dr. Gould's view these strong con- 

 trasts indicate periodic fluctuations, and an 

 elaborate discussion of the facts at his dispo- 

 sal sustains the theory of a mutual relation. 

 " It is manifest," Dr. Gould remarks, " that 

 if the variations of the terrestrial temperature 

 follow those of the sun-spots, and are thus ade- 

 quate to account for the correspondence ob- 

 served between these and the variations of the 

 magnetic declination, all necessity for assum- 

 ing any direct and transcendental connection 

 between this latter and the disturbance of the 

 solar surface disappears." 



The Transit of Mercury. A transit of Mer- 

 cury occurred on the 6th of May, 1878, the pas- 

 sage occupying 7 h> 33 m> . The phenomenon was 



generally observed under favorable conditions. 

 Prof. S. P. Langley of Allegheny, Pa., saw the 

 entire disk of Mercury outside the sun at least 

 half a minute before the first external con- 

 tact. This visibility was regarded as due to 

 the brightness of the coronal background. A 

 remarkable difference was noticed between 

 the apparent size of the planet before and 

 after its entrance upon the sun; the former 

 being greater than the latter in the ratio of 

 five to four. Prof. Langley saw no " black 

 drop" nor "ligament." He failed also to see 

 the central bright spot, as well as the aureola 

 around the planet phenomena observed by 

 several other astronomers. 



A comparison of the best contact-observa- 

 tions obtained at different stations gave new 

 evidence in favor of Leverrier's theory of the 

 motion of Mercury's perihelion, and of the ex- 

 istence of a cause of perturbation between 

 Mercury and the sun. 



Relative Brightness of Venus and Mercury. 

 On September 26, 1878, Mercury and Ve- 

 nus were so close together that they were 

 telescopically in the same field of view. Mr. 

 James Nasmyth of Kent, England, improved 

 this favorable circumstance by making careful 

 comparisons of the relative brightness of the 

 two planets. The result of the observation 

 was that Mercury has less than half the bright- 

 ness of Venus, or, in other words, less than half 

 the reflective power. This relative deficiency 

 is the more remarkable when it is considered 

 that, in consequence of Mercury's nearness to 

 the sun, its brightness ought to be nearly four 

 times greater than that of Venus. The fact 

 seems to indicate an important difference be- 

 tween the atmospheres of the two planets. 



The Satellites of Mars. In a memoir re- 

 cently published by the Washington Observa- 

 tory, Prof. Asaph Hall has discussed all the 

 observations of the satellites of Mars, and has 

 determined the elements of their orbits within 

 very narrow limits of probable error. The 

 name Phobos has been adopted by Prof. Hall 

 for the inner satellite, and that of Deimos for 

 the outer. In brightness the former is rated 

 by the discoverer as an ll^-magnitude star; 

 the latter as of the 12th. The diameter of 

 Deimos is estimated by Prof. Pickering of 

 Harvard Observatory at six miles, that of Pho- 

 bos at seven. At Washington alone 43 obser- 

 vations of Phobos and 52 of Deimos were ob- 

 tained up to October 25th, when they could no 

 longer be detected by the 26-inch equatorial. 

 The periods and eccentricities derived from 

 these observations are as follows : 



Phobos. Deimos. 



Period 7h. 39m. 15 OTs. 30h. ITm. 53'86s. 



Eccentricity 0'0328 0-005T4. 



Not only are the orbits approximately circu- 

 lar, but the planes of both are very nearly co- 

 incident with the equator of Mars. 1*he mass 

 of Mars obtained from the Washington ob- 

 servations is uvjrgl.TTrg-- 



Minor Planets. Twelve minor planets were 



