ALTERATIONS OF THE SOLAR LIGHT. ] ^J 



sage, when the disk of the sun appears yellow, orange, or 

 red. 



Mr. Hassenfratz concluded, that the observation of the This to be don* 

 solar spectrum produced by the refraction of the prism J- ^sn^'^ 

 would lead him to his object, because, the spectrum being tram, 

 necessarily incomplete from the absence of the rays inter- 

 cepted in their passage, the determination of the deficiencies 

 in the spectrum would indicate these; and it might after- 

 ward be ascertained whether the colour resulting from a 

 mixture of the rays remaining would be the same as that of 

 the solar disk. * 



Mr. Hassenfratz cites several results of the experiments he observations 

 made under the various circumstances of which we are made, 

 speaking. Thus on the 13th of January, 18Q7, having ob- 

 served the spectrum at ten o'clock in the morning, he found, 

 the violet wanting, with part of the indigo. "Now accord- 

 ing- to Newton's rule, if the violet be suppressed, with a cer- 

 tain portion of the indigo, the remaining colours are those, 

 which, by their mixture, produce yellow: and the disk of 

 the sun appeared of the latter colour. As a necessary con- 

 sequence, the yellow of the spectrum was deeper than ordi- 

 nary. The same day at noon, the sun was white, and the 

 spectrum then had its whole extent. But at four in the 

 evening the violet had disappeared anew, with a greater 

 quantity of indigo, so that the sun appeared of a deeper 

 yellow than at ten in the morning. Lastly, at a quarter 

 after four the spectrum was shortened on the same side, and 

 in consequence the solar disk inclined to orange. 



Mr. Hassenfratz presented to the class several coloured Drawings of 

 drawings of the solar spectrum, such as he observed them in tllc spectrum 

 circumstances where it had lost more or less of its length. ta etU 

 The drawings were made at the moment of the experiment 

 by Mr. Gerard, at the Polytechnic School. 



The author adds, that he has sometimes remarked the Subtraction of 



effects of the subtraction of several rays in rainbows seen at ra y s from tlie 

 itp i n i i i-ii i -i • i ■ • rainbow. 



dmerent hours ot the day, which nave exhibited varieties 



in the number or extent of the coloured arcs. 



The experiments are interesting in themselves, because 



they serve to explain in a natural and satisfactory manner 



some phenomena, on which we had not any thing precise. 



they 



