THE EXPEDITION AT TALNI. 5 



the tropics. It soon became a regular item of the evening's 

 programme to map out the contour of the Light and form 

 estimates of its intensity; and we supplemented these by a few 

 observations of the morning branch of the Light before sunrise. 

 The voyage down the Red Sea, December 24th to 27th, 

 was especially memorable. The early mornings afforded 

 Mr. Evershed welcome opportunities for testing his slit spec- 

 troscope. His cabin was on the east, the port side, of the 

 ship, and his berth pointed tx> the porthole. It was thus 

 very simple for him to affix his spectroscope to the under- 

 side of Mr. Thwaites' berth, which was above his own, so 

 that the light from the porthole fell directly on the slit. The 

 trifling inconvenience which this otherwise excellent arrange- 

 ment caused Mr. Thwaites was, of course, cheerfully borne in 

 the interests of science, and Mr. Evershed obtained some very 

 satisfactory photographs of the Fraiinhofer lines as a test of the 

 focus of his instrument. In the evening, just before sundown, 

 the spectroscopes were brought into work on the starboard side, 

 the great telluric bands coming out like storm-clouds in the 

 >l^ctrum of the setting sun ; whilst the moment when the sun's 

 image was diminished to a single narrow segment was most 

 admirable for bringing my own little spectroscopic opera -glass 

 into perfect focus. Then, as the sun's rim dipped, we crossed 

 to the port side, and watched the sharply defined outline of the 

 earth's shadow creep upward and obliterate the rose and purple 

 of the eastern sky. Next came the search for Mercury, which 

 was usually found by the naked eye within half an hour of sunset, 

 and ere he sank the starry host began to gather. A little later, 

 and the Zodiacal Light came out like a second twilight, soon to 

 be followed by the less brilliant radiance of the Milky Way. 

 The two met on the horizon, their axes probably intersecting at 

 the place of the sun, now sunk considerably below it. Here the 

 Light quite overpowered its rival. When full darkness had come 

 on, the two were seen intersecting each other at almost the oppo- 

 site point of the heavens ; but here the Light had faded to the 

 most evanescent faintness. In the early evening both objects 

 ca>t a broad path of light on the waters. That from the zodiacal 

 glow soon faded out, but as the night deepened the star-shine 

 from a score of brilliants made miniature moon-tracks to every 

 part of the horizon. We were now travelling nearly due south, 

 and a mere glance at the sky on each successive evening was 

 quite sufficient to show how rapidly the Pole Star sank, and 

 the new stranger southern constellations rushed up from the 

 under-world. 



" And the Southern Cross, like a standard flying, 



Hangs in the front of the tropic night ; 

 But the Great Bear sinks like a hero dying, 

 And the Pole Star lowers its signal light." 



