C2843 



XIV. Experiments on the Refrangibility of the invisible Rays of the 

 Sun. By William Herschel, LL. D. F. R. S. 



Read April 24, 1800. 



In that section of my former paper which treats of radiant heat, 

 it was hinted, though from imperfect experiments, that the range 

 of its refrangibility is probably more extensive than that of the 

 prismatic colours ; but, having lately had some favourable sun- 

 shine, and obtained a sufficient confirmation of the same, it will 

 be proper to add the following experiments to those which have 

 been given. 



I provided a small stand, with four short legs, and covered it 

 with white paper.* On this I drew five lines, parallel to one end 

 of the stand, at half an inch distance from each other, but so 

 that the first of the lines might only be ^ of an inch from the 

 edge. These lines I intersected at right angles with three others ; 

 the 2d and 3d whereof were, respectively, at 2y and at 4 inches 

 from the first. 



The same thermometers that have before been marked 

 No. 1, 3, and 3, mounted upon their small inclined planes, were 

 then placed so as to have the centres of the shadow of their 

 balls thrown on the intersection of these lines. Now, setting 

 my little stand upon a table, I caused the prismatic spectrum to 

 fall with its extreme colour upon the edge of the paper, so that 

 none might advance beyond the first line. In this arrangement, 



» See Plate XI. 



