100 METHOD OF EXAMINING DISPERSIVE POWERS. 



Curious effects By candle-light, a different fet of appearances may be dif- 



tf cindTe^igt^ tIn S ui(hed - When a ver y nar ™w B*« of the blue light at the 

 lower part of the flame is examined alone, in the fame manner, 

 through a prifm, the fpeclrum, inftead of appearing a feries of 

 lights of different hues contiguous, may be feen divided into five 

 images, at a diftance from each other. The lft is broad red, 

 terminated by a bright line of yellow; the 2d and 3d are both 

 green ; the 4th and 5th are blue, the lad of which appears to 

 correfpond with the divifion of blue and violet in the folar 

 fpeclrum, or the line D of Fig. 3. 

 and the light of When the object viewed is a blue line of electric light, I 

 electricity. have found the fpeclrum to be alfo feparate4 into feveral 



images; but the phenomena are fomewhat different from the 

 preceding. It is, however, needlefs to defcribe minutely, ap- 

 pearances which vary according to the brilliancy of the light, 

 and which I cannot undertake to explain. 



and di ("oxy- 

 genating rays 

 on the conjine 

 of violet. 



on one fide there are inviiible rays occafioning heat, that are lefs re- 

 frangible than red light j and on the other 1 have myfelf obferved, 

 (and the fame remark has been made by Mr. Ritter,) that there are 

 likewife inviiible rays of another kind, that are more refracled than 

 the violet. It is by their chemical effecls alone that the exiftence of 

 thefe can be difcovered j and, by far the moil delicate teft of their 

 prefence is the white muriate of filver. 



To Scheele, among many valuable difcoverles, we are indebted 

 for having firft duly diftinguifhed between radiant heat and light ; 

 (Trait e de l" Air et du Feu, § 56", 57 j) and to him alfo we owe the 

 obfervation, that when muriate of filver is expofed to the common 

 prifmatic fpre&rum, it is blackened more in the violet than in any 

 other kind of light. (§ 66.) In repeating this experiment, I found 

 that the blacknefs extended not only through the fpace occupied by 

 the violet, but to an equal degree, and to about an equal diftance, 

 beyond the vifible fpectrum ; and that, by narrowing the pencil of 

 light received on the prifm, the difcoloration may be made to fall 

 almoil entirely beyond the violet. 



It would appear therefore, that this and other effects ufually at- 

 tributed to light, are not in fact owing to any of the rays ufually 

 perceived, but to invifible rays that accompany them ; and that, if 

 we include two kinds that are invifible, we may diftinguifh, upon 

 the whole, fix fpecies of rays into which a fun-beam is diviiible by 

 refraction. 



VI. An 



