ii.] HIS NEW MAP. 17 



parts. The line at B is very distinct, and of a considerable thickness. 

 From B to c may be reckoned nine very delicate and well-defined 

 lines. The line at c is broad and black like D. Between c and D 

 are found nearly thirty very fine lines, which, however, with the 

 exception of two, cannot be perceived but with a high magnifying 

 power and with prisms of great dispersion ; they are besides well 

 defined. The same is the case with the lines between B and c. 

 The line D consists of two strong lines separated by a bright one. 

 Between D and E we recognise eighty-four lines of different sizes ; 

 that at E consists of several lines, of which the middle one is the 

 strongest. From E to b there are nearly twenty-four lines ; at b 

 there are three very strong ones, two of which are separated by a 

 fine and clear line; they are among the strongest in the spectrum. 

 The space b F contains nearly fifty-two lines, of which F is very 

 strong. Between F and G there are about 185 lines of different 

 sizes ; at G many lines are accumulated, several of which are re- 

 markable for their size. From G to H there are nearly 190 different 

 lines. The bands at H are of a very singular nature; they are 

 both nearly equal, and are formed of several lines, in the middle 

 of which there is one very strong and deep. From H to i they 

 likewise occur in great numbers. Hence it follows that in 

 the space BH there are 574 lines, the strongest of which are 

 shown in the figure. The relative distances of the strongest 

 lines were measured with the theodolite, and placed in the figure 

 from observation. The faintest lines only were inserted from 

 estimation by the eye." 



Here then we have the first substantial contribution to 

 a map of the newly discovered lines in the spectrum of 

 the sun. 



Fraunhofer next explained why the lines are not well 

 marked, and why they disappear if the aperture of the 

 slit becomes too large. If the aperture is not such that the 

 light which passes through it cannot be regarded as a single 

 ray, or if the angle of the width of the aperture is greater 

 than that of the width of the line, then the image of the 

 same line will be projected several times parallel to itself, and 



C 



