NATURAL PHILOSOPHY. 105 



acid, a luminous figure appears, resembling the hilt of an ancient 

 sword. 



Without going into further detail, what has been here described will 

 sufficiently show how interesting the results are which have been ob- 

 tained by the different experiments. Prof, von Kobell has named 

 these beautiful luminous appearances after their first discoverer, our 

 illustrious countryman, Brewster. He calls them " Brewster'sche 

 Licht-figuren," which may most fitly be rendered by " Brewsterian 

 Light Figures." 



THE COMPOSITION OF LIGHT AND THE LAW OF HARMONIOUS 



COLORING. 



In a work published some time since, on " Chromotography," by Mr. 

 Field of London, the author has described an experiment by means of 

 which he considers he has determined the proportion of colored rays 

 which constitutes white or solar light. The problem, the solution of 

 which Mr. Field has attempted, is admitted to be one of the most deli- 

 cate and unmanageable in the domain of physical science, and phi- 

 losophers who have instituted experiments and speculated on the sub- 

 ject from Newton, in former days, to Brewster and Herschel, in our 

 own time have felt and confessed the difficulties which beset the in- 

 quiry. It is well known that Newton, from his famous experiment 

 with the prism, concluded that white or solar light is composed of seven 

 colors of different refrangibility, which he named violet, indigo, blue, 

 green, yellow, orange, and red. He also measured the size of the 

 variously-colored portions of the spectrum, in order to ascertain the 

 amount of colored light in the sunbeam. Should we admit with New- 

 ton that white light is made up of no fewer than seven parts, still the 

 difficulty of measuring the colored spaces of the spectrum is great, if, 

 indeed, the task be not quite a hopeless one. It is hardly possible to 

 find two persons who see so nearly alike that they can agree as to 

 where one color ends and the next begins, and thus no two estimates 

 of the colored spaces are likely to be the same. A notable instance of 

 variance is afforded in the values assigned to the snaces by Newton 

 and Fraunhofer. While they are at one in their opinion of the size of 

 the orange and indigo spaces, the former finds the yellow and violet to 

 be in the ratio of 40 and 80, whereas the latter assigns them the very 

 different ratio of 27 and 109. No subsequent observer has ventured 

 to alter either estimate, and no one who is familiar with the spectrum 

 will put much faith in any measurement of it, by whomsoever or with 

 what care soever it may have been made. 



Another analysis of light was afterwards made by Dr. Wollaston, a 

 high authority in optical questions. As he employed a narrow beam 

 of light, he obtained a spectrum which consisted apparently of only 

 four colors, namely, red, green, blue, and violet ; and on dividing the 

 space occupied by the spectrum into 100 equal parts, he found these 

 colors to occupy respectively 16, 23, 36, and 25 of the divisions. A 

 single narrow band of yellow, dividing the red from the green space, 

 was all he could detect, and he hastily concluded that this color was 

 merely a mixture of red and green, and consequently not a primary 

 and important element in the composition of light. This statement of 

 Wollaston's analysis shows how widely the observations of this observer 

 differed from those of Newton. 



