Tlie Theory of Temvporary Stars. 3 



found no trace of bright lines or bands on his plates ; the broad 

 hazy absorptions were displaced towards the violet by an amount 

 corresponding to a velocity of 700 kilometers per second towards 

 the sun. By the 24th the typical /lova spectrum was fully estab- 

 lished. It differed slightly from that of Nova Aurigae, showing 

 the bright bands much broader, and the dark ones less dark 

 relatively to their surroundings, than they appeared in the 

 spectrum of the earlier star.^ These bands, in addition to the 

 lines of hydrogen, included the "enhanced lines" of iron, calcium 

 and magnesium, and (possibly) D.^; H and K showed both as 

 bands and as fine lines. 



3. — Bearing of the Earliest Observations on Theory. 



This may be summed up as follows : — 



1. The star, when near the maximum, was certainly exceed- 

 ingly hot. The coincidence of the tirst spectrum with that of 

 the Orion stars establishes this fact, which is even better 

 attested by its great extension into the ultraviolet and 

 the high relative intensity of that portion. The presence of 

 "enhanced line" absorptions proves the same thing. 



2. The change to a typical nova spectrum, though rapid, was 

 gradual. Pickering, on the basis of his own photographs, 

 regards it as " very sudden " ; but the coincident work of Vogel 

 shows that the dark bands mad« their appearance before the 

 bright ones, and that at first they were feeble ; consequently the 

 setting up of the typical spectrum seems to have had nothing 

 catastrophic about it. 



3. Pickering- calls attention to a possible experimentum crjicis 

 for deciding between the rival theories. He points out that, on 

 the collision hypothesis, the maximum separation of the bright 

 and dark bands should occur at the epoch of maximum bright- 

 ness, and considers that the comparison of his second and third 

 photographs shows that the separation had increased between 

 23rd and 24th February — i.e., after the maximum was passed — 

 and consequently the collision hypothesis cannot be true. 



1 Pickering (Ap. J., xiii., Plate iv.) reproduces the spectra of the two stars. 

 - Ap. J., xiii., p. 277. 



lA 



