382 Frofessor H. E. Turner [June 5, 



chance, and embarked on an exposure of 36 hours. Think of all 

 that is implied ! Such an exposure must of course be spread over 

 several nights. After guiding the telescope with minute care for 

 9 long hours on one night and closing up the plate carefully before 

 approaching dawn could impress it in the faintest degree, the astro- 

 nomer cannot yet have the satisfaction of developing the plate and 

 the relief of knowing that it is successful : he must return to his 

 vigil on the next fine night and to his self-denial on its morrow ; 

 and so on for several nights. Mr. Perrine was at work altogether 

 on four, and only after all this labour and suspense did he in the 

 dark-room — 



•'.... dare to put it to the touch 

 To win or lose it all." 



for it was quite possible, of course, that there would be nothing on 

 the plate after all, if the brightness of the nebula had been over- 

 estimated. How many men are there qualified by an equal experi- 

 ence to appreciate Mr. Perrine's anxiety while that plate was being 

 developed ? or his joy when it proved successful and a new fact was 

 given to the world ? 



Turning now to the spectrum of the new star itself, we have 

 learnt to ask by the spectroscope two questions : firstly, what is the 

 source of light made of ; and secondly, how quickly is it approaching 

 us or receding from us ? 



There are two sets of similar lines side by side in the spectrum of 

 new stars, one set bright, the other dark ; indicating firstly a mass 

 of hot hydrogen (for instance) itself shining ; and secondly a mass of 

 cooler hydrogen in front of a source of light, forming dark lines 

 by absorption. From the relative position of the lines it would 

 appear that the cool hydrogen is approaching us very rapidly — 

 something like 1000 miles a second faster than the hot. And this 

 suggests an explosion of some kind. We must not be alarmed by 

 the magnitude of the velocity, nor even by its persistence, for Nova 

 Persei is so far away, that even a velocity of 1000 miles per second 

 continued for six months will look quite small : it would not suffice 

 to carry a particle outside the patch which the star makes on a 

 photographic plate. 



Giving free scope to the possibilities as regards the scale of 

 these magnificent phenomena, I will venture to collect the main facts 

 enumerated in a single hypothesis for the origin of a new star ; and 

 I will ask my audience kindly to remember that the case is not yet 

 considered ripe for judgment. 



Far away from us — so far away that the winged-messenger Light 

 only bring us news of the occurrence centuries afterwards — a star 

 wandering through space, enters a vast " dark nebula." The friction 

 of the encounter raises the temperature of the star enormously 

 within a day or two, just as a meteor, on entering our tenuous upper 

 atmosphere is set ablaze in a second or two. The hydrogen and 



