1866.] SMALL WOOD — PRESIDENT'S ADDRESS. 131 



proportion as to the quantity of the different coloured rays, to that 

 which starts from the incandescent light-giving surface. Sodium, 

 magnesium, hydrogen, and probably iron, have been found in this 

 star ; and even a photograph on wet collodion has been obtained. 

 In reference to double stars, observations on Beta Cygni and 

 Alpha Hercules confirm these observations. 



Various opinions have been ventured on the composition of the 

 nebulae. It has been affirmed that they are masses of minute 

 stars, and only require higher optical powers to reduce them to 

 distinct vision. The construction of Lord Rosse's telescope was 

 looked forward to as tending to set the matter at rest ; but, 

 instead of this, it seemed to involve the question in still greater 

 difficulty. Its solution was not lost sight of during the past year, 

 and the spectrum observation has been shown to have an impor- 

 tant bearing on the nebular hypothesis of the cosmical origin of 

 the universe. It shows that the elementary substances must have 

 existed in different proportions at different points of the nebulous 

 mass ; otherwise, by condensation, equal portions of the elements 

 from the surrounding vapour would have been collected. 



There is also an analogy to the manner in which the components 

 of the earth's crust are distributed, for some of these elements are 

 widely diffused through vegetable, animal, and mineral matter. 



It has been further shown that it is only liquid and solid 

 bodies that give out a continuous spectrum ; while gases alone, 

 when rendered luminous by heat, give out light which, after 

 dispersion by the prism, is found to consist of certain degrees of 

 refrangibility only, and which appear as bright lines on a dark 

 ground, contrary to the solar spectrum, which shows dark lines on 

 a bright ground. This fact has shown that, in the nebulae, large 

 masses of gas exist, and they possess no resemblance whatever to 

 stars or clusters of stars. The nebulae, therefore, are not masses 

 of stars removed to such a distance as to render them irresolvable, 

 but consist, for the most part, of luminous gases. 



This presents to us, at once, another instance of unity in nature, 

 by recognizing; each of the simple bodies held in suspension in the 

 flame, whose rays are decomposed by the prism. The dispersion 

 of the sun's rays by the prism forms the standard of observation ; 

 any deviation will shew either bright lines in the place of dark 

 ones, or dark lines in the place of bright ones. Nickel, chromium, 

 magnesium, iron, potassium, sodium, barium, copper, cobalt and 



