ASTRONOMICAL PHENOMENA AND PROGRESS. 



41 



Stewart, and Loewy. A table exhibiting the 

 number of sun-spots recorded at Kcw during 

 yoar 1809, after the manner of Ilofrath 

 Schwaiie, has boon sent in to the Astronom- 

 ical Society, and published in their monthly 

 notices. M. Otto Struve, director of the Im- 

 perial Observatory at Pulkowa, visited Eng- 

 land in the month of August last. He brought 

 with him, tor the Kew Observatory, some sun- 

 pieiurcs taken at Wilna with the photohelio- 

 graph, which was made some years ago, under 

 the direction of Mr. Do La Rue, by Mr. Dall- 

 meyer. This instrument combines several im- 

 portant improvements on the original Kew 

 model, the value of which is forcibly brought 

 out in the superior definition of the Wilna 

 sun-pictures. As, however, the series of the 

 ten-yearly record at Kew was commenced with 

 the instrument as originally constructed, it 

 was not deemed desirable to alter it in any 

 \vay until the series had been completed and 

 reduced, and the corrections for optical distor- 

 tion ascertained and applied. In the event of 

 the sun-work being continued after 1872, it 

 will be desirable to do so with a new and im- 

 proved heliograph. M. Struve proposed to ex- 

 change the complete series of pictures obtained 

 at Wilna for that made at Kew. He also stated 

 that it is contemplated to erect a second helio- 

 graph at the Central Observatory at Pulkowa. 

 A Solar Phenomenon accounted for. In a 

 letter read before the Royal Astronomical So- 

 ciety, in March, Lieutenant Herschel gave a 

 description of some singular object which he 

 had seen traversing the sun's disk, October 

 17 and 18, 1869 : 



He was about to apply his spectroscope to the ob- 

 servation of a solar prominence when his attention 

 was attracted to certain shadows traversing the disk 

 of the sun, which became bright streaks when they had 

 passed beyond it. At first he thought these appear- 

 ances were due to sparks in the tube of the telescope, 

 but the phenomenon lasted too long for this explana- 

 tion to be available. He next thought that perhaps 

 a system of meteors might be in transit, and prepared 

 to subject the phenomenon to careful scrutiny. The 

 equatorial was set in motion, the sun's disk being 

 ;ed on a screen. The shadows were seen per- 

 y tnnvrs'mg the solar disk, but at different 

 velocities, the larger ones travelling most swiftly. 

 There appeared to oe two streams. He noticed that 

 when the sun was in focus the objects were indis- 

 und that they appeared very distinctly when 

 he focussed on a distant cloud. At length, while 

 he was attentively scrutinizing the phenomenon, he 

 saw one of the objects come suddenly to a stand-still 

 and then whisk off in a different direction ; and then 

 ho perceived that the phenomenon he had been ex- 

 amining with such anxious care was not in reality an 

 astronomical phenomenon at all, but consisted merely 

 of a flight of locusts. He considered, however, that 

 not only was the existence of so enormous a swarm 

 of locusts as the duration of the stream indicated an 

 interesting fact in itself, but that we might find in 

 the occurrence the explanation of many statements 

 which had been made respecting meteors supposed 

 to have transited the sun, and also of some pecu- 

 liarities noticed by astronomers in America during 

 the total eclipse of last year. Mr. Stone said that it 

 was important when appearances of this sort were 

 noticed that the observer should examine, as Lieu- 

 tenant Herschel had done, whether the objects seen 



in transit required the tame focus M the sun. Thin 

 wan the bent way of determining whether the ob- 

 jects were terroBtrud or not. 



Photograph of a Solar Prominence. Prof. 

 C. A. XOUfi of Dartmouth College, thus 

 records a successful attempt to procure a 

 photograph of a solar prominence, at any time 

 and without waiting for the favorable oppor- 

 tunity of a total eclipse. He writes to the 

 American Journal of Science, under date of 

 September 28, 1870 : 



" I have just succeeded, with the help of 

 our skilful artist, Mr. II. O. Bly, in obtaining 

 a photograph of one of the solar prominences, 

 a copy of which I enclose. It was taken 

 through the hydrogen line, near G, by open- 

 ing the slit of the spectroscope and attaching 

 a small camera to its eye-piece. As a picture 

 of course it amounts to very little. It required 

 an exposure of three minutes and a half, and, 

 the polar axis of the telescope being imper- 

 fectly adjusted, the clock-work failed to fol- 

 low perfectly, so that no detail is visible, and 

 the picture will not bear much magnifying. I 

 am convinced, however, that by using a more 

 sensitive collodion, and taking proper pains 

 with the adjustment of the instrument, satis- * 

 factory photographs of these curious objects 

 may be obtained. 



"I may add that the spectroscope employed 

 has the dispersive power of 13 prisms of flint, 

 each with an angle of 55." 



Solar Prominences easily seen. Mr. Ernest 

 Carpmael, of Streatham Hill, England, has 

 succeeded in obtaining good views of the solar 

 prominences by the following simple instru- 

 mental agency: He fixed one of Mr. Brown- 

 ing's direct-vision spectroscopes (having seven 

 prisms) on a board which also carried a two- 

 inch object-glass belonging to a good field 

 telescope, and mounted the instrument, thus 

 arranged, on the back of an ordinary bedroom 

 mirror, and directed it at the sun. The slit 

 was set so as nicely to divide the D line, and 

 a blue glass was generally interposed in front 

 of the slit to sift the light. As the image of 

 the sun traversed the slit at intervals, the 

 flames appeared as bright prolongations of the 

 F line extending beyond the sun's limb. It 

 was also clearly seen at times that these pro- 

 longations were narrower than the F line, and 

 were not in the centre of it, also that they 

 were frequently detached from the sun's limb, 

 and sometimes they were not straight : ap- 

 pearances depending, as is generally supposed, 

 on the velocity and pressure of the gas in the- 

 flame. The flames were also readily seen iti 

 the C line. In observing the solar spectrum 

 he has found colored glasses in front of the 

 elit very useful to shut out as much as possi- 

 ble of the light from the parts of the spectrum 

 not under observation. By using the spectro- 

 scope without its slit and collimating lens, and 

 directing it toward the great nebula in Orion, 

 it shows close together three bright images of 

 the nebula exhibited on a continuous spectrum. 



