TRANSACTIONS OF THE SECTIONS. 1 § 
*: he least value of - that is, its value for the violet ray, there will be no 
sorption ; if greater, some one ray or more will be at minima. Let 
suppose the medium such that 26 =m, for any ray. Then, in 
ing from one end of the spectrum to the other, the changes of 
ensity and maxima and minima which may occur, will depend on 
e number of changes which the cosine will go through in passing 
rom its value in the violet ray to that in the red; or, supposing X, i, 
in 
v 
the wave lengths for these rays, from cos 2 7 m to cos 2 7m jy 
f r 
_ through all the intermediate values. The intensity will have as many 
‘Maxima and minima as the cosine has values = + 1, and=—1. And 
_ this number may be increased as much as we please, by supposing (7), 
_ or, what is the same thing, (4) taken sufficiently great. 
_ The formula was, in the first instance, deduced for the simpler sup- 
position of a single medium. It is then shown, that if we suppose a 
compound of several media which have separately different values of 
_ 6, the resulting formula will still preserve the same condition of de- 
_ pending on the changes of the cosine, and each medium will retain its 
_ own set of maxima and minima. 
The investigation is conducted in the first instance on the supposition 
_ of the internal successive reflexions taking place only between two par- 
_ ticles, or sets of particles, or reflecting surfaces. The author next pro- 
eeds to the case where more such are taken into account, and de- 
_ duces a formula more complex, but which results in such a form that 
the maxima and minima are seen to depend on exactly the same condi- 
_ tions as in the simpler case. In certain cases of the absorption of 
gases, &c. appearances of a regular and systematical character are pre- 
_ sented, and Von Wrede shows that at least a general explanation of all 
these is afforded by the principles here developed; that is, merely by 
assigning particular values to 6, and supposing those values different in 
_ the different simple media of which the compounds are made up. 
_ He also points out one method by which a rough approximation 
_ eyen to a numerical comparison may be effected: it applies very satis- 
factorily (as far as it goes) to the case of the iodic gas spectrum. 
Besides this, the author describes an experiment in which the effect 
‘of one or two internal reflexions is imitated by means of plates of 
‘mica, and dark bands in consequence produced in the spectrum. 
_ The principles adopted by Von Wrede appear to be quite conform- 
able to what may most reasonably be supposed to take place in the 
passage of a ray through a transparent body. But so little have the 
phenomena been reduced to any laws, that we are not yet in a condi- 
tion to make any satisfactory comparison of observation and theory. 
The grand object of inquiry must be to obtain, if possible, some nu- 
erical laws, expressing the disposition and arrangement of the bands 
‘the spectrum; and in cases where they are apparently destitute of 
symmetry, to examine carefully whether any hypothesis of several 
_ sets superposed will reduce the apparent confusion to order. 
_ VOL. vi. 1837. c 
