AURORA BOREALIS. 



49 



constructed by them for the Naval Observa- 

 tory, Washington. Four years were allowed 

 for its manufacture, the contract having been 

 made in 1870; but every part of the work 

 was completed earlier than agreed upon. 

 Chance & Brother, of Birmingham, cast the 

 object-glass, which was ground and polished 

 by the Messrs. Clark. It has a clear aperture 

 of 26 inches. The metallic base and the in- 

 strument itself weigh about six tons, and the 

 focal length is nearly 32 feet. The new tele- 

 scope is poised on a dome 40 feet high and 41 

 feet in diameter. The instrument cost $50,- 

 000, appropriated by Congress. It was placed 

 in position without the least accident. No 

 official report has yet been made of its work- 

 ing. The Mi-.ssrs. C'lark have received an 

 order from Mr. McConnick for another tele- 

 scope of the same size as that at the Capitol, 

 designed as a gift, it is reported, to Washing- 

 ton and Lee University, Virginia. 



The Lalande Medal Prof. James C. Wat- 

 son, of the University of Michigan, who has 

 been highly successful in the discovery of as- 

 teroids, has received a valuable gold medal, 

 awarded him by the Institute of France. The 

 Ann Arbor Segitter says: 



The medal was awarded to Prof. Watson by the 

 Institute of France, in July, 1870, but, on account of 

 the war, its completion and transmission were de- 

 layed. It was made at the French Mint, and accom- 

 panying it was the certificate of the director of the 

 mint, as to its fineness and weight, as well as 225 

 francs in bills of the Bank of France, being the un- 

 expended balance of the sum appropriated by the 

 Institute for the medal. It is exquisitely wrought. 

 and has on one side a bust of Minerva in half relief, 

 surrounded by the words : ' Institut Imperial do 

 France, Conntit., Art. Ixxxviii." The other side 

 has inclosed in a massive wreath the following 

 -: " Acadt'mie des Sciences, Prix d' Astro- 

 nomic, fondation Lalande, Jauiea Craig Watson, 



isea." 



AURORA BOREALIS. A very brilliant 

 aurora was seen, April 18th, over a large part 

 of England, and scientific observers coramuni- 

 oatfd many interesting facts with regard to it 

 to the press. Mr. A. S. Herschel enjoyed a 

 good view of the phenomenon at Carlisle, and 

 records his impressions of it at length. The 

 first manifestation of the aurora took place at 

 9 P. M., in a clear sky, in the form of a bri-rht, 

 white arch, divided into low streamers. From 

 this presently arose tall but faint shafts of 

 light, which, later on, changed to a deep rose- 

 color, and from that to ricli crimson, some of 

 them having the intensity of fire. The light 

 at one time was so great that Mr. Ilcrschd 

 pould read his watch and correct his note- 

 book by it. The spectrum of the red stream- 

 ers, like that of the white, he examined with 

 a small pocket spectroscope, and found in it 

 only the nsnal bright greenish line which was 

 very vivid in cvrry j>h;isc of the display. The 

 author thus describes the spectacle at its 

 height, and thence to the close : 



Both the arches and streamers were stationary, 

 and [>r<-s.-ntfil no sensible tendency to motion, how- 

 ever slow, while they were visible. At this time the 

 TOL. mi. 4 A 



brightening streamers began to flicker in their light. 

 Waves of light, rising from the north, succeeded 

 each other rapidly, and appeared to flow swiftly over 

 them toward the zenith. Arch after arch was visible 

 as the waves passed over them, and fitful gleams 

 among the auroral masses overhead shot to and fro 

 there, like flashes of summer lightning. The rays 

 and wisps of the corona, and belts or fragments of 

 the aurora overhead were rendered especially lumi- 

 nous by these discharges. Farther from the zenith, 

 in the north, the waves rose smoothly and steadily, 

 with a motion that was indeed very swift, but it was 

 yet quite distinctly discernible, and more easily dis- 

 tinguishable there than in their passage overhead. 

 The arches or belts of the streamers appeared to be 

 lighted up instantaneously, as they were reached. 

 Although their intermixture in the north made it 

 very diflicult to decide this clearly, yet the upward 

 progress of the waves there was very evident, while 

 no such ascending movements could be distin- 

 guished in the cast and west quarters of the sky. 

 The belts and arches stretching toward those parts 

 of the horizon, through the zenith, and past, or 

 through the corona, forming the termination of the 

 aurora toward the south, were constantly lighted up 

 by momentary flashes, extending almost simultane- 

 ously along their whole lengths. The brightness 

 of the flashes in those parts of the aurora which in- 

 cluded the corona, and arches or lateral branches 

 extending from it toward the magnetic east and west 

 points, is easily accounted for by the belts and clus- 

 ters of streamers in those positions being seen " on 

 edge," or "end on," extremely foreshortened by 

 perspective, so that the increase of light along their 

 whole heights appeared to be concentrated, when 

 the waves overtook them, to a single flush. The 

 motion of the waves must be extremely swift, as 

 they scarcely occupied more than a second in pass- 

 ing from an altitude of about 45' to the zenith. 

 Supposing that (as the best observations of them 

 have frequently agreed in showing) the heights of 

 auroral arches, and of the bases of auroral streamers, 

 are usually about 100 miles above the earth's sur- 

 face, the velocity of propagation of these waves of 

 electrical disturbance from north to south cannot 

 have been much less than 100 miles per second. 

 Such a prodigious velocity cannot possibly be as- 

 cribed to waves in the upper atmosphere driven by 

 winds among its rarefied strata, to which the sweep- 

 ing motion of the light waves, apparently wafted by 

 gusts among the streamers, otherwise Lore a very 

 singular resemblance. 



At 9' 84 some of the strongest waves passing 

 across the corona lighted up a faint white arch in 

 the south, extending from Arcturus across the 

 northern part of Virgo to the head of Leo, several 

 degrees in width. At 9" 87, when the wave-dis- 

 turbance, mfter continuine in full activity for about 

 ten minutes, ceased us rapidly as it began, this arch 

 and the corona still remained faintly visible ; but, 

 together with all the other arches and streamers of 

 any altitude lately lighted up by the waves, they 

 soon vanished, and the whole appearance nf the sky 

 at 9" 40 was about the same as when the aurora 

 was first seen. At 9 h 43 m , however, the northern 

 sky was again crowded in every part with thin, 

 white streamers scattered indiscriminately over it, 

 like groves of slender fir-trees on a hill-side, among 

 which one very sharp and bright rny shone for a 

 few seconds, springing from the horizon to a con- 

 siderable altitude in the west. At 9" 55 all con- 

 spicuous streamers had disappeared, leaving only a 

 general glow, among the brighter parts of which the 

 wave -disturbance began again, and with less in- 

 tensity than before, but with the same regularly as- 

 cending motions; the undulations succeeded each 

 other without intermission until 10* 5 ; they then 

 censed, and the faint appearances of the aurora, 

 which were visible after this time, were, so far as I 

 could observe them, until half-past eleven o'clock, 

 of a very insignificant and inconspicuous character. 



