1 ( M2] The Ottawa Naturalist. 53 



blue stars are much hotter. The temperature cited is that of 

 the outer visible radiating surface, that of the interior must be 

 inconceivably hotter. Such enormous differences of tempera- 

 ture between the stars and the absolute zero 460F. of space 

 must inevitably produce a turbulent seething system with up- 

 rushes and outbursts of the hotter vapors from the interior 

 producing violent eruptions examples of which, though prob- 

 ably on a comparatively mild and small scale are given by the 

 solar prominences. 



Try and picture to yourselves such a body as I have des- 

 cribed. A turbulent seething mass of gases and vapors at a 

 temperature even on the outside several times as high as we 

 can get on the earth and of almost inconceivable size up to 

 50 million or more miles in diameter. Even the most vivid 

 imagination must fall far short of the stupendous reality. 



Having this picture in our minds let us return to the nebulae 

 and before going on with their development let us also have in 

 our minds their appearance. I have a number of photographs 

 of the nebulae, made by reflecting telescopes, which show us 

 much more than can be seen visually and indicate the varied 

 and complex structure of these objects. 



Starting then with a nebula of comparatively simple form, 

 whether gaseous or meteoric in character is immaterial, as the 

 result will be the same, we have it condensing and growing 

 smaller under the action of gravity and hotter under the conver- 

 sion of work into heat. As the temperature rises it begins to 

 glow, the more volatile elements are vaporized it becomes more 

 nearly spherical in form and is a deep red star giving a banded 

 or fluted spectrum, indicating the presence of chemical com- 

 pounds only existent at moderate temperature. As condensa- 

 tion proceeds the body gets hotter and yellower, the flutings dis- 

 appear from the spectrum, and large numbers of metallic lines, 

 characteristic of the second type of spectrum, similar to our own 

 sun, appear. At this stage the star is still very tenuous, probably 

 considerably less dense than our own atmosphere, and at a 

 temperature of about 10,000F. 



Further condensation with its resultant increase of tem- 

 perature has the effect of driving to the outer atmosphere the 

 more volatile and lighter elements such as hydrogen and helium 

 and thus diminishing and suppressing the metallic lines resulting 

 in a much simpler spectrum containing very broad and dense 

 hydrogen lines and a few faint metallic lines and in some stars 

 the hydrogen lines only. The star is now white or bluish white 

 in color the temperature is from 15,000 to 18,000 F., and if 

 the body is of moderate size, about the same as our sun, it has 

 eached the height of its evolution, its maximum temperature; 



