ASTRONOMY AND METEOROLOGY. 845 



veloped in Antares. These obscure and ill-defined bands are inde- 

 pendent of the metallic lines, and may be compared to those pro- 

 duced by the gaseous terrestrial atmosphere in the solar spectrum 

 near the horizon, and they may have a similar origin. The two 

 systems, therefore, the one formed by five metallic rays or lines, 

 and the other by black gaseous bands, are independent of each 

 other. 



Spectrum of the Aurora Borealis. — According to M. Otto Struve, 

 it consists of one line, so that the light is monochromatic. The line 

 falls near the margin of the yellow and green, about the position 

 1,259, on Kirchhoffs map. 



WATER ON THE PLANETS AND STARS. 



Janssen thinks he has noticed the presence of the spectrum of 

 the vapor of water in several of the stars, among them, Antares. 

 The spectrum of this star presents very plainly the lines and bands 

 of the vapor of water, the lines being black, very broad, and with 

 the characteristic position. He has taken into account the error 

 proceeding from the moisture of the air ; he has made trials on the 

 heights of Mt. Etna, where the air is very dry, and at Palermo 

 and Marseilles. He has also observed evidence of the presence 

 of the vapor of water in the atmosphere of Mars and Saturn. 



This latter result is particularly interesting. It may be remem- 

 bered that the planet Mars shows bright areas at its poles, alter- 

 nately increasing and decreasing, appearing precisely in the same 

 manner as our own earth would looli at a great distance ; having, 

 during the winter season, its northern polar region covered with 

 snow and ice much farther toward the equator than during our 

 summer season. Hence it has long been concluded that the planet 

 Mars is covered with water, just like our earth. From other ob- 

 servations it has long been known that Mars, Jupiter, and Saturn 

 are surrounded by gaseous atmospheres. By the above observa- 

 tions of Janssen, the presence of water on Mars is now finally 

 proved ; as the seasons change on the planet, its polar regions are 

 more or less enveloped in ice, just as here on the earth, and at all 

 times the watery vapor in the atmosphere of Mars is seen in the 

 spectrum of the planet, as we notice the vapor of our atmosphere 

 in the spectrum of the setting sun. 



Janssen concludes his report with the following remarks : " To 

 the close analogies which already unite the planets of our system, 

 a new and important character has just been added. All these 

 planets form, accordingly, but one family; they revolve around 

 the same central body giving them heat and light. They have 

 each a year, seasons, an atmosphere, and on many of the planets 

 clouds have been observed in these atmospheres. Finall}', water, 

 which plays so important a part in all organized beings, is also an 

 element conmion to the planets. These are powerful reasons to 

 think that life is no exclusive privilege of our little earth, the 

 younger sister in the great planetary family." 



