Ch. XVni.] TEOPICAL SKIES. 307 



incomparable Sirius, and its ally, Orion, are common to 

 both latitudes. 



It is not so much, however, the southern sky as the 

 tropical sky which is so striking to one coming from 

 northern latitudes. In any high latitude, the density and 

 irregularity of the atmospheric strata produce those rapid 

 changes in refraction which cause the twinkling so con- 

 spicuous among the stars of our own sky — a phenomenon 

 not without its own character of beauty, owiug to the 

 brUliant and changing colours which accompany each suc- 

 cessive change of refraction. But as we approach the 

 tropics, the stillness and clearness of the air produce this 

 result in a less and less degree, so that under favourable 

 conditions the uniformity and purity of the atmosphere 

 transmit the light of the stars with little sensible disturb- 

 ance, and hence this beautiful diamond-like scintillation is 

 more or less lost, and gives place to a placid and calm star- 

 light, in which each orb seems to shine with the steady light 

 of a planet, and another element of beauty is substituted for 

 that which has been lost. 



But when the full moon comes upon the scene and 

 extinguishes, the lesser stars in its effulgent rays, the 

 tropical night is a sight to be remembered ; and especially 

 at sea, when the long track from the ship to the horizon is 

 bathed in bright, dancing light — ^not dazzling, like the sun 

 — but white and sUvery, and such as mortal eyes can look 

 upon without blinking. 



The close oppressive air between the decks on such nights 

 often encourages the sailor to carry his mattress into the 

 open air, and sleep under the canopy of the sky — a proceed- 

 ing not altogether without danger if no awning be spread, 

 inasmuch as heavy dews often fall, and rheumatic affections 



X 2 



