E. B. Hunt on the Dispersion of Light. 369 



magnitude. It then begins again to increase, and in 3£ hours 

 more is restored to its usual brightness, going through all its 

 changes in 2 d 20 h 48 m or thereabouts."* Light occupies more 

 than 7,500 times as long in reaching us from the parallactic 

 limit beyond which Algol lies, as Algol does in changing between 

 its maximum and minimum brightness- If we suppose V r to be 

 be l-7500th greater than V v , the red maxima would reach us 

 simultaneously with the violet minima and conversely. Even 

 this value would completely confuse the star's periodicity; and 

 by increasing it, this peculiarity would be rapidly obliterated. 

 These varving phases, marked with no chromatic changes or con- 

 iusion, show beyond appeal that the extreme spectral elements of 

 the light from Algol, cannot have velocities of transmission differ- 

 mg by even near l-7500th their mean. How utterly incom- 

 petent then is any possible difference between the velocities of 

 the different colored rays to explain dispersion. In the chro- 

 mate of lead the dispersion is about one-fifth of the maximum 

 refraction: compared with which any possible difference of chro- 

 matic velocities along the same line of media is wholly insig- . 

 nificant. 



It seems needless farther to accumulate evidence of the fact 

 that the rays of different colors, have in nature, velocities too 

 nearly equal ever to serve for the explanation of dispersion. If 

 M. Cauchy has shown that the hypothesis of finite intervals, 



fi 



oonjl 



ematics. A powerful direct argument against this hypothesis as 

 a fact in nature, is furnished by Ehrenberg'S microscopic investi- 

 gations into infusorial physiology. By a combination of actual 



ies, he concludes! that in 

 certain cases of young monads, "the partitions of these monad- 

 bellies will be but 1-4,800,000 to 1-6,400,000 of a French line 

 in diameter, &c. I have besides seen rudiments of eyes in the 

 monads to which I have given the name of Microglena Monadina, 

 and which are 1-192 of a line in diameter. These often fire- 

 red eye-points, appear in large infusoria, to be a line granular 

 red pigment, but whose granules perhaps first covered by many 

 fine pigment granules, are small lenses, &e. : and although I will 

 not lay particular stress on the fineness of these parts, yet the ex- 

 istence of eyes, however rudimentary they may be considered, 

 allows of the possibility that even in the smallest species they 

 may be present, and tends to lead us to a not so proximate finity 

 of organic molecules ; it may even give a useful hint for consid- 

 erations on the elements of colors and the theory of light." This 



* Sir J. F. W. Herschel, Treatise on A-tronomy. 

 f Taylor scientific Mei >ifs, vol. i, Art, 28, p. 514. 



Secoxd Seeies, Vol. VII, No. 21.— May, 1849. 47 



