J.uiuARY 2, 1899.] 



KNOWLEDGE. 



9 



your feet. As a consequence you are continually plunging 

 and slipping into some deep hoof-mark in the mud. You 

 suddenly feel a wet stinging slap, and you find your face 

 has formed a barrier between the horse's wet tail and a 

 villainous fly on his flank. The perspiration is streaming 

 off you, and your back is aching unbearably. Just as 

 you are beginning to think that you must give it up 

 to stretch your back at any cost, the patero suddenly 

 stops. The relief is great as you squat down, and your 

 surprise is greater when you take the field glasses, and 

 looking under the horse's belly discover that the birds are 

 quite close. Before proceeding further a rope is fastened 

 to the halter, passed between the horse's legs and tied to 

 its tail. (Fig. 5.) This is a necessary precaution to ensure 

 the horse keeping his head down. Were he to raise it 

 when so near the birds they would probably become 

 alarmed. At last you get within shooting distance, the 

 signal is given, the horse stops, and, cocking your gun, 

 you stand up. The relief to your cramped and aching 

 back is so great that for a moment you stay stock still and 

 survey the birds to which the calnsti-o and his master have 

 brought you so cleverly and so successfully. Now the 

 unsuspected danger suddenly dawns upon the flock — there 

 is a straining of necks and a flutter of wings. Raising 

 your gun you fire over the horse's back, or, if there is 

 time, rush out from behind him and fire in the open. 

 The well-trained cabestro never moves while you shoot. 

 Drooping his head, he remains like a block of wood imtil 

 the spoU is collected and you return to him. 



These beloved cabestros were our constant companions 

 during our stay in the marismas and many were the birds 

 we watched, photographed and shot from behind them. 



WITT'S PLANET DQ. 



ONE of the most important astronomical discoveries 

 of recent years is the finding of the planet DQ, 

 by Witt. This object will come nearer to the 

 Earth than any other similar object, except the 

 Moon. Its minimum distance is about fifteen 

 million miles, and the corresponding parallax nearly a 

 minute of arc. To determine the photometric brightness 

 of this object, the stars, — C-SoG^, — 0°o579, — 0-5600, 

 — 0^.5608, and — 6"5(>26 were each measured on five 

 nights with the meridian photometer, eight settings being 

 made each night, with the resulting magnitudes, 7'87, 

 8-G5, K-71, 8-50, and 9-57, respectively. The probable 

 error of these values varies from ±0-020 to ±0-033. The 

 brightness of the stars, — 6^5u50, — (')°55(i0, and — ()°5588 

 was later determined difi'erentially from these, with the 

 resulting magnitudes 8-80, 9-89, and 8-37. Mr. Wendell 

 compared the planet on six nights by means of the photo- 

 meter with achromatic prisms attached to the fifteen-inch 

 equatorial. The number of settings on each night was 

 forty-eight. On September 5th and Gth, 1898, it was 

 compared with -— 6°5026, on September 9th with —6^5608, 

 on September 12th with — 6''5579, and on September 13th 

 and 1-lth with — 6°5588. The resulting magnitudes were 

 12-19, 11-97, 12-10, 12-01, 12-20, and 12-29. Mean, 

 12-13 ±0-04. As the logarithms of the distances of the 

 Sun and Earth, on the mean date, September 10th, were 

 0-2360 and 9-9115, the magnitude when these distances 

 are both unity becomes 11-39. 



It is not easy to obtain photographs adapted to deter- 

 mining the photographic brightness of this object, owing 

 to its faintness and rapid motion. With a short exposure 

 the image is very faint, and with a long exposure a trail 

 is obtained which cannot be compared with the circular 



images of adjacent stars. Measures of the photographic 

 brightness have been made by Mrs. Fleming on plates 

 taken with the eight-inch Draper telescope, and having 

 exposures of about fifteen minutes. The planet was not 

 far distant from the variable star T Aquarii and was com- 

 pared with four of its comparison stars whose photometric 

 magnitudes had already been determined. Plates taken 

 on September 6, 12, 13, 13, 13, 13, 14, 17, 20, and 21, 

 1898, gave the magnitudes 12 78, 12-75, 12-80, 12-85, 

 12-78, 12-75, 12-75, 12-72, 12-65, and 12-68. Mean, 

 12-75 ±001. Similar measures of two isochromatic plates 

 taken on September 17th and 20th, gave the magnitudes 

 12-80 and 12-61. Mean, 1270 ±0-08. Since the planet 

 is fainter photographically than photometrically, it is 

 probable that its colour, like that of the Sun, is redder 

 than an average star. 



Several interesting photometric problems present them- 

 selves in connection with this object. First, the approxi- 

 mate diameter may be determined by comparison with the 

 brighter asteroids and satellites, assuming that the 

 reflecting power is the same. Secondly, the great variation 

 in the distance of this object from the earth will aflbrd an 

 excellent test of the law that the light varies inversely as 

 the square of the distance. The existence of an absorbing 

 medium in the solar system will thus be tested. Thirdly, 

 owing to the proximity of this object to the Earth at 

 opposition, its phase angle will vary by a large amount. 

 It will, therefore, afi'ord an excellent test of the law 

 connecting this angle with the variation in brightness, 

 which has been found by two or three observers indepen- 

 dently. 



NEBULA IN ANDROMEDA. 



A comparison of photographs of the nebula in Andromeda 

 taken with the eight-inch and eleven-inch Draper 

 telescopes on September 20th and 21st, 1898, with similar 

 photographs taken in 1893, 1894, 1895, and 1890, fails to 

 show the new stellated appearance recently announced by 

 Seraphimoff, of Pulkowa. See also Astnm. Xach. 147, 

 p. 223. Edward C. Pickering. 



Harvard College Observatory. 



CONSIDERATIONS ON THE PLANET SATURN. 



By E. M. Antoniadi. 



RECEIVING from the sun less than one-ninetieth 

 of the heat sent us from that luminary, the 

 thermal conditions of the planet Saturn, supposed 

 destitute of intrinsic heat, or of a heat imprisoning 

 atmosphere, cannot be much above the absolute 

 zero of temperature. Lavoisier, who clearly foresaw the 

 eventual liquefaction of gases, upon examining what would 

 take place if our earth were transported to the distance of 

 Saturn from the sun, suggested the idea that our refriger- 

 ated atmosphere would alter its gaseous state and con- 

 dense itself into a liquid or solid mass upon the planet's 

 surface. The subsequent liquefaction of sulphurous acid 

 gas by Monge and Clouet in 1800, that of chlorine by 

 Northmore in 1805, and, above all, the liquefaction of 

 oxygen, hydrogen, and carbonic acid gas by MM. Caillette 

 and Raoul Pictet in 1877, is merely the experimental 

 verification of a physical conception whose force lay in its 

 anticipating the unknown. 



As a consequence, we find that, in virtue of their great 

 distances from the sun, the four superior planets, if not 

 self-hot, would be deprived of atmospheres, comparable at 

 least in composition to our own. The presence of gaseous 

 envelopes round these worlds would thus imply relative 

 youth in their planetary evolution. 



