136 Dr BREWSTER on a New Analysis of Solar Light. 



EXPLANATION OF PLATE II. 



Fig. 1. Represents the Red spectrum, which enters into the composition of the solar 

 spectrum, and extends along the whole of it. The maximum intensity is 

 opposite R. 



Fig. 2. Represents the Yellow spectrum of the same length. Its maximum intensity 

 is opposite Y. 



Fig. 3. Represents the Blue spectrum of the same length. Its maximum intensity 

 is opposite B. 



Fig. 4. Represents the Solar spectrum, formed by the union, or superposition, of 

 the three preceding figures. 



This figure is intended merely for illustration, and not as an accurate 

 picture of the solar spectrum. The proportion of the coloured spaces is, 

 however, very nearly that which FEACTNHOFER determined by examina- 

 tion through a telescope. The fixed lines discovered by this eminent 

 philosopher are omitted. 



Fig. 5. Differs from Fig. 4 only in the relative forms of the three curves R, Y, and 

 B, whose ordinates are supposed to represent the intensity of light at dif- 

 ferent points of each of the three simple spectra. Their form is entirely 

 empirical, though it cannot be very different from the truth. FRAUNHOFEE 

 has determined from observation the general curve of illumination for the 

 whole solar spectrum ; and though there is no method of determining the 

 ratio of the three ordinates, ax, bx, ex, Fig. 4. at any point of the spec- 

 trum, yet the sum of these ordinates, ax + bx + ex, must always be equal 

 to the ordinate of the general curve at the same point x, as determined by 

 FRAUNHOFEK. 



