THE NEW STAR IN THE MILKY WAY. 54.3 



if large bodies are dealt with, the cooling must take a very long 

 time. 



The latest view put forward is, that these bodies are produced 

 by the sudden meeting in space of two swarms or streams of 

 meteoritic matter, each traveling with a considerable velocity, 

 the sudden bright light being due to the collisions of the particles 

 composing the swarms ; and this hypothesis explains very well 

 not only the sudden outburst, but the rapid decrease in bright- 

 ness, due to the fact that only small particles are dealt with, and 

 these must cool and dim quickly. 



The appearance of the present new star, or "Nova," in the 

 constellation of Auriga, was first announced by an anonymous 

 post-card received at the Royal Observatory, Edinburgh. Why 

 the post-card was sent anonymously remains a mystery ; but the 

 extraordinary reticence of the writer does not make any differ- 

 ence to the immortality of the discoverer ; for while, on the one 

 hand, newly discovered comets, which are also of an apparently 

 temporary nature, are always associated with the names of those 

 who first observe them, new stars, on the other hand, are al- 

 ways referred to by the name of the constellation in which they 

 appear. 



The instrument now used to obtain observations of these 

 strange visitors consists of a combination of an object-glass ; a 

 prism, which is placed outside the object-glass, and a camera. The 

 function of the prism is to separate the million strands of colored 

 light which go to make white light ; that of the object-glass is to 

 collect each color, concentrating it at the same time, so that finally 

 we get a fine line of rainbow color. 



This method of obtaining a spectrum is by no means modern, 

 but was suggested and used by the German optician Fraunhofer 

 about the year 1814. He placed a prism before the object-glass 

 of a theodolite, and in this way was the first to observe the spectra 

 of some of the stars. By the use of this method, whether the eye 

 or the photographic plate is used, the so-called " spectrum " of the 

 body under observation can be studied without any difficulty. 

 The length of the exposures required when photography is em- 

 ployed for stars of different magnitude varies very considerably ; 

 for the brightest a few minutes are generally ample, but for those 

 of much smaller magnitude a space of two or three hours is by no 

 means too long. 



The spectra that are thus obtained are of various kinds, as 

 various classes of so-called stars are observed. Some consist' of 

 bright lines on a dark background, others of dark lines on 

 a bright background while a mixture of both these is met 

 with. These variations in spectra depend upon the fact that 

 any substance that is heated sufficiently to emit light whether 



