104 



THE NATURALIST. 



The solid matter, on being incinerated, gives one and one-fourth, to one 

 and one-half per cent, of ash, which consists of one-half of sea-salt, one-tenth 

 of peroxide of iron, and the rest of lime, magnesia, potash, soda, phosphoric 

 acid^ and carbonic acid. 



Having thus far imperfectly explained the nature and chemical compo- 

 of the blood, as at present known, we shall now proceed to a consideration 

 of the nature and phenomena of the colour, respecting which an observation 

 made by Hoppe, followed by a most beautiful and scientific investigation by 

 Professor Stokes, has recently thrown a new light on this abstruse branch of 

 physiological inquiry. We think the readers of the Naturalist will feel 

 some interest in a sketch of the results which have accrued to physiology 

 from the discovery. This we give all the more willingly, because we believe 

 that it has not hitherto received that amount of attention from physiologists 

 that its interest and importance demand. 



If a pure ray of white light from the sun, or, for the sake of experiment 

 at any time, from a lamp, be admitted into a dark room through the triangular 

 piece of glass, called a prism, the ray as it emerges from the prism is seen 

 to have undergone a most peculiar change. Instead of being refracted 

 altogether and appearing still as a white ray, it is divided into several rays of 

 very vivid colours. In this state it is said to be analyzed, or decomposed into 

 its elementary rays. Each ray has its own peculiar tint, so that the number 

 of possible shades of colour is, as far as we know, infinite ; but f®r practical 

 purposes we may and do divide them into seven distinct colours, viz., — red, 

 orange, yellow, green, blue, indigo, and violet. White light is the result of 

 the union or blending together of these various colours. IsTow, when a white 

 ray passes through a prism, the coloured rays of which it consists are bent 

 or refracted, and the peculiarity of the matter is that each coloured ray is 

 refracted at a different angle, the red least, then green, and violet the most 

 of all. The result is that if a sheet of white paper be held up on the side 

 of the prism furthest from the light, and in a pecuKar position, we see re- 

 flected upon it, not a pencil of white light, but a regular series of colours all 

 blending into one another, the red being at one end and the violet at the 

 other. This is the phenomenon which has risen within the last few years into 

 such immense scientific importance, under the name of solar or prismatic 

 spectrum. 



It was observed by Hoppe that, if a weak solution of blood was inter- 

 posed between the light and the prism, the spectrum was no longer 

 continuous. 



