MISCELLANEOUS PAPERS. 371 



masses. The relation of comets to meteoric showers has been estab- 

 lished within recent years. 



The radiometer and spectroscope have given us valuable data re- 

 garding the condition and stages of the so-called fixed stars. There 

 are at least three well-defined classes — those of the Sirian, the solar 

 and the a Herculis types. The first are whitish stars, whose spectra 

 are marked by bright lines, the dark lines indicating hydrogen, or by 

 the violet and ultraviolet colors. This represents an early stage of 

 stellar development, some indeed seeming to be mere aggregations of 

 nebulous matter. Those of the solar type have spectra rich in dark 

 lines of many elements, and represent a maturer condition. Those 

 of the last type indicate rapidly cooling suns, and are marked by red- 

 dish or other pronounced spectral tints. There has not been much 

 advance made along the line of measurement of distances, the paral- 

 laxes of hardly a hundred stars being definitely determined. Enough 

 has been accomplished, however, to give us the general distances and 

 to show that there is no definite relation between size and proper 

 movements and distance. 



The temporary stars that occasionally flash out brilliantly and then 

 die down to invisibility have long been subjects of interest and specu- 

 lation. During the fall of 1890 a new star appeared in Perseus and 

 rapidly grew in brightness until it reached the first magnitude. It 

 then faded away, but, luckily for the interests of science, has been fol- 

 lowed assiduously and its various changes carefully recorded and 

 photographed. Nova Persei was thus found to have developed into 

 a rapidly swelling nebulous mass whose swift centrifugal motion re- 

 sembled, and even surpassed that of an explosion. It is believed that 

 it arose from the collision of two so-called dark stars whose impact 

 not only shattered them, but transformed them into lambent gases. 

 It is believed by many that this nebulous mass will in time cease its 

 expansion, and then begin to condense under the efiPect of gravity, 

 giving rise to a new stellar system, under the working of the laws of 

 the modified nebular hypothesis. Perhaps this may represent one 

 stage in an endless cycle of stellar evolution, which normally includes, 

 collision, nebulous mass, rotating spiral, a central mass with various 

 attendant satellites, and finally a darkened star. This at least is be- 

 lieved by many notable investigators. 



Until within the latter half of the past century, the nebulous 

 masses revealed here and there were considered star clusters, too far 

 away for our telescopes to resolve into their constituent stars. The 

 spectroscope, however, proves most of the persistent nebulous masses 

 to be really gaseous and meteoric in form. They are probably the 

 world-stufF from which suns and planets are made. This is somethin 



