Nov. 21, 1889] 



NATURE 



69 



is, sixty-six days ; but if these small spots be considered we find 

 an interval of twenty-five days without spots — namely, from April 

 II to May 5. The minimum period, therefore, appears to have 

 passed about the end of April, this being the time when the 

 greatest number of days passed without spots being observed on 

 the sun. The new period opened with the appearance of a large 

 spot on June 16. 



Return of Brorsen's Comet.— The following elements 

 and ephemeris for this comet are given by Dr. E, Lamp in 

 Asfronomische Nachrichten, No. 2933 : — 



T = 1890 February 24*1358 Berlin midnight. 



The Companion of 77 Pegasi. — A companion to r; Pegasi 

 was discovered by Sir William Herschel in 1780, and sub- 

 sequently observed by South in 1824. Its magnitude has been 

 rated from twelve to fifteen. Mr. S. W. Burnham, however, 

 notes (Astrotiomische A^achrichten, No. 2933) that, using the 

 36-inch refractor at the Lick Observatory, the Herschel com- 

 panion appears as a close double. South's mean of two measures 

 is given in his catalogue as : — 



1824-84 338° "9 89" 82 2« S. 



The following is the mean of four measures made at Mount 

 Hamilton : — 



t\ Pegasi. 

 B and C. A and BC. 



1889-53 83°-3 o"-29 lo-i lo-i I 1889-53 339°-o 9o"-38 

 The close pair is difficult, and can hardly fail to be a physical 

 system, and Mr. Burnham thinks that, although it is not a test 

 for the large telescope, it will not be seen with any small instru- 

 ment. 



General Bibliography of Astronomy. — The second 

 part of Vol. I. of this comprehensive bibliography has been pub- 

 lished. It represents Houzeau's last work, and hence it is well 

 that his biographical note, by A. Lancaster, should be included. 

 The first part of Vol. I., published in 1887, contained the 

 references to historical works and those relating to astrology ; 

 the part just published contains the references to biographies of 

 astronomers and their epistolary communications, general astro- 

 nomical works, astronomical societies and their proceedings, and 

 everything relating to spherical astronomy. Works on theoretical 

 astronomy are also well represented. The third and last part of 

 Vol. I. is now in press, and contains references to all the pub- 

 lished matter on the mechanism of the heavens, physical, 

 practical, and descriptive astronomy, and the systems of cos- 

 mogony. The utility of this bibliography, when completed, 

 needs no comment. 



J. C, Houzeau's " Vade Mecum."— With reference to our 

 biographical note on J. C. Houzeau (p. 20), M. A. Lancaster 



writes to remind us that Houzeau's "Vade Mecum " was issued 

 after the appearance of the second volume of the " Bibliographic 

 Ge'nerale de I'Astronomie," the publication of which began in 

 1879. Moreover, the "Vade Mecum" was only a second 

 edition of the "Repertoire des Constantes de I'Astronomie," in- 

 serted in 1877 in the first volume of the new series of the 

 " Annales Astronomiques " of the Brussels Royal Observatory. 

 The numerous materials brought together for the " Bibliographie 

 Generale " suggested to Houzeau the idea of issuing a new 

 edition of the "Repertoire" considerably corrected and en- 

 larged. 



A New Comet. — A new comet was discovered on Noven>- 

 ber 17 by Mr. Lewis Swift, of the Warner Observatory, Roches- 

 ter, New York. Place at November 17, 6h. 35m. 2s. G. M. T. ; 

 R.A. = 22h. 42m. 24s. ; N.P.D. = 78° 9'. Daily motion in 

 R.A., -f 2m. ; in N.P.D,, — 15', The comet was only faint. 



MIRAGE IN THE SOUTH AMERICAN 

 PAMPAS. 



WAS staying in the Pampas of the Argentine Republic, near 

 Melincue, a small town of the Province of Santa Fe, from 

 September 1888 to March 1889, During my stay I had the 

 opportunity of observing certain mirage phenomena. It is 

 possible that my notes may contain .something of interest. 

 They were, designedly, taken without reference to any previous 

 knowledge of the theory of mirage that I might possess. 



To illustrate my observations I had drawn eight diagrams ; 

 but, for the purpose of insertion in Nature, I have been 

 obliged to reduce these to two. Hence I fear that my descrip- 

 tions may not be as clear as I should wish. 



The most general conclusion at which I arrived was that 

 there were two classes of mirage of very different character. 

 The one I shall call "the summer mirage," the other "the 

 winter mirage." I would observe that, without a telescope of 

 some sort, one would be unable to make observations of much 

 value ; and that, as I had but a binocular telescope, in many 

 details I failed to make out as much as I could had I possessed 

 a larger telescope steadily mounted. 



I, The Summer Mirage. 



(i) This mirage is seen in full day. I was told that in normal 

 years it is most remarkable in the extreme heat of summer. 

 The summer of December, January, and February 1888 and 

 1889 was abnormally wet, however. And I myself saw the 

 mirage most frequently in spring (September, October, and 

 the earlier part of November), the grass being then short and 

 very dry. Later on the grass became very long, and unusually- 

 green and damp, owing to the heavy rains. And then I saw 

 the mirage but rarely in the grass plains, though on the several 

 occasions on which I passed, in the blaze of a summer day, the 

 dry sandy bed of an old laguna, the mirage was there to be 

 seen very clearly. 



On one or two occasions in spring I saw the mirage when there 

 was a fairly cold wind and no perceptible sunshine, but still in 

 full day. 



(2) This kind of mirage usually appeared as a strip of " water "' 

 running more or less parallel to the horizon, at one end narrow- 

 ing to a point, and at the other end opening out into the sky. It 

 appeared much as an arm of the sea, or an estuary, seen near the 

 horizon, and running parallel to it. The "water" was of the 

 same colour as the sky above it near the horizon. 



(3) Viewed through glasses, the whole of the land seen above 

 and beyond the "water," the "water" itself, and to a less 

 extent the land seen just this side of it, appeared wavy and ill- 

 defined, flocculent, and (when there was any breeze) possessed 

 of a drifting movement down the wind. At the thin end of the 

 " water," and just beyond it in the line of the layer, one could 

 see broken fragments of " water " drifting over the land ; and, 

 in like manner, the peninsula of land appeared to end in a line 

 of drifting fragments. 



(4) It appeared to me that the land seen beyond the watery 

 layer was either within the limits of the natural horizon, or not 

 much beyond them. One did not, as one did in the "winter 

 mirage," see houses, &c., that were normally out of sight. 



(5) Cattle, &c., seen in the watery layer were ill-defined. But 

 on the whole it seemed that their legs were hidden, and bodies 

 were reflected inverted, much as if they had been standing iij 

 shallow water. 



