1870.] Astronomy. 95 



spectrum. Professor Harkness also found that the corona gives a 

 bright-line spectrum, but. superposed on a continuous one. Now 

 when we combine Professor Young's observation with Angstrom's 

 discovery that the Zodiacal Light gives the same spectrum as the 

 Aurora, it becomes one of the most interesting, and at the same time 

 one of the most perplexing, ever made by astronomers. A bright-line 

 spectrum indicates gaseity, and we cannot believe the corona to be a 

 gaseous solar envelope, nor indeed to be gaseous at all, if we accept 

 Lockyer's observations. Nor can one understand the Zodiacal Light 

 to be gaseous. 



Perhaps, however, all these observations may be reconciled by 

 regarding the spectrum of the corona to be not necessarily indicative 

 of the gaseity of this object in its entirety. Electrical discharges 

 taking place between the particles (probably solid) of which the 

 Corona and the Zodiacal Light consist would give a spectrum of 

 bright lines. Then also we could understand the continuous 

 spectrum seen by Professor Harkness, since the bodies forming the 

 corona would reflect the solar light. 



The whole subject is, however, at present full of difficulty and 

 perplexity. In future eclipses the corona will doubtless attract a 

 large share of the observer's attention. 



Another result of the American eclipse observations has been 

 the suggestion by Professor Young of a new mode of observing the 

 coming transit of Venus. It was found that the approach of the 

 moon to the sun's limb was cognizable before the moment of actual 

 contact, owing to the gradual obliteration of the bright lines belonging 

 to the spectrum of the chromosphere ; and Professor Young suggests 

 that the approach of Yenus might be observable in the same way in 

 1874 and 1882. There are, however, many difficulties in the applica- 

 tion of this method. In particular the method applies to external 

 contacts, and the preparations hitherto made have had reference to 

 internal contacts. At some of the best places for observing internal 

 contacts, external contacts will not be observable at all. Then 

 astronomers are not quite certain at what part of the sun's limb 

 contact will take place, nor at what angle Yenus will cross the limb. 

 These circumstances would leave the spectroscopist small chance of 

 success in an observation of so delicate a nature. 



It remains to be seen, however, whether spectroscopic observa- 

 tion may not be applicable in other ways. For example, Mr. 

 Huggins has suggested that instead of the slit being placed at right 

 angles to the sun's limb, it should be placed tangentially. Mr. 

 Proctor has recommended an open slit, placed tangentially so as to 

 include the solar cusps before internal contact. These cusps would 

 give two continuous spectra, the approach of which towards each 

 other would indicate the moment of internal contact more exactly 

 than the approach of the cusps. 



