50 ASTRONOMICAL PHENOMENA. 



floor of that crater. Previous to February, 

 1869, 15 had been recorded, of which 6 have 

 been observed recently. In and since Febru- 

 ary, 1869, 9 additional spots have been ob- 

 served, of which 6 have been more or less con- 

 stantly seen by two observers. The remaining 

 13 ha"ve either become invisible, or are but 

 rarely seen. Certain peaks on the western 

 wall of the crater Plato have been measured 

 by Beer and Madler, and their height found 

 to be from 5,000 to 7,000 English feet. These 

 peaks, at sunrise, cast well-defined, long shad- 

 ows, which have been measured by Professor 

 Chailis, of Cambridge. The shadows of the 

 three principal peaks come in proximity to 

 three very minute craters on the floor of Plato, 

 thus furnishing a means of identifying these 

 craters at any future time. 



Transits of Venus. Preparatory arrange- 

 ments were made in England during the 

 year for the efficient observation of the impor- 

 tant transit of Venus, which will take place 

 in December, 1874. Numerous stations have 

 been selected for observing the phenomenon in 

 its various stages and conditions. For observ- 

 ing the ingress of Venus upon the sun's disk, 

 as accelerated by parallax, Owhyhee and the 

 neighboring islands, the Marquesas Islands, the 

 Aleutian Islantls, and the mouth of the Amoor, 

 are regarded as more or less favorably situated. 

 For observing the ingress retarded by parallax, 

 Kerguelen Island and Croyet's Island are well 

 situated, though geographically unfavorable. 

 Next in order come Rodriguez, Mauritius, and 

 Bourbon Islands, Madras, and Bombay. The 

 egress accelerated by parallax can be best ob- 

 served in Auckland Islands, Canterbury, Wel- 

 lington, and Auckland, Norfolk Island, Mel- 

 bourne, and Sydney ; while Omsk, Orsk, Astra- 

 khan, Erzeroum, Aleppo, Smyrna, and Alex- 

 andria, are highly suitable places for noting 

 the retardation of the egress by parallax. Mr. 

 De La Rue has been investigating the practica- 

 bility of taking photographs of Venus in tran- 

 sit, at several well-separated stations, as an 

 auxiliary means of estimating the sun's dis- 

 tance. He points out that the close corre- 

 spondence between the result obtained by 

 micrometrical measurements applied to his 

 eclipse photographs in 1860, and the elements 

 calculated by Mr. Farley, in the Nautical Al- 

 manac, show that a very close approximation 

 to the truth is to be looked for in the case of 

 the transit of Venus. The difficulty of meas- 

 uring the solar and lunar disks presented in 

 an eclipse photograph is very much greater 

 than that attending the corresponding measure- 

 ments in a transit photograph. Moreover, the 

 observer of a transit would not be hurried like 

 the observer of an eclipse, since the former 

 phenomenon is several hours in progress, while 

 the latter lasts but a few minutes. The photo- 

 graphing could be as easily done as that which 

 occurs daily at the Kew Observatory. Mr. 

 Stone, of Greenwich, suggests that the three 

 following points should be carefully attended 



AURORA BOREALIS. 



to in making the telescopic observations ; that 

 telescopes of nearly the same aperture should 

 be employed; that magnifying powers should 

 be nearly the same ; and that attention should 

 be directed to observations of real internal 

 contact as the chief points. By " real internal 

 contact," he means the formation of the " black 

 drop," as it is called, simultaneously with the 

 complete ingress of the planet upon the solar 

 disk. The transit of 1874 does not afford the 

 same opportunity which was had in that of 

 1769, for estimating the sun's distance from the 

 different duration of the transit as observed 

 from different points of the earth's surface ; 

 nor is there a probability, according to Mr. 

 Airy's calculations, of applying that method in 

 the transit of 1882. The latter transit, as well 

 as that of 1874, takes place in December, 

 when the southern or sea hemisphere of the 

 earth is turned toward the sun. The transits 

 of 1761 and 1769 (the most important observed 

 last century) happened in June, when the 

 northern hemisphere was .bowed to the sun. 

 Stations for observing the transit of 1882 have 

 already been chosen. 



Transit of Mercury. The recent transit of 

 Mercury was observed by Mr. Row (a Hindoo 

 astronomer), at Vizagapatam. The observer 

 and some of his friends noticed that near the 

 middle of the transit a " wavy tint of light " 

 darted from the upper edge of the planet. This 

 light was occasionally disturbed, but continued 

 visible for some time. No change of focal 

 length or of the eye-piece employed had any 

 effect on the phenomenon. It is said to be the 

 first instance of the kind occurring during a 

 transit of Mercury. 



AURORA BOREALIS. An auroral display of 

 extraordinary extent and splendor occurred on 

 the night of April 15th. It was seen through- 

 out Canada, being especially brilliant at St. 

 John, N. B., Montreal, and Toronto, in the 

 north and middle western part of the United 

 States, and in the upper portion of the South- 

 ern States. At Boston the spectacle was re- 

 markably fine between 7 and 8 p. M., surpass.- 

 ing in richness and beauty any previous exhi- 

 bition of the kind at that point for many years. 

 The Western Union Telegraph Company oper- 

 ated their lines in that city without the aid of 

 a battery, and the same was done in many 

 other places. From Philadelphia to Pittsburg 

 the telegraph lines were worked by the auroral 

 electricity alone. At Cincinnati it was noticed 

 that all the lines, except those running south 

 and west, were disturbed, the currents being 

 sometimes too strong, and at others almost 

 neutralized. The operation of lines at St. John, 

 N. B., was seriously interfered with, and com- 

 munication almost entirely ceased between 

 Plaister Cove and Heart's Content, N. B. 

 The phenomenon, as seen at Richmond, Va., 

 is described as a belt of white, apparently 

 about six feet wide, extending across the sky 

 from east and west, drifting northward, and 

 finally gathering as a fan closes, and then dis- 



