i 
q 
OF THE SOLAR SPEGTRUM. _ 557 
ment which gives rise to a separation of the two electricities 
necessary for maintaining the molecular equilibrium, and the 
‘neutralization of which forms the flashes we observe, we may 
consider the action of the solar rays on these bodies as analogous 
to that of these rays on bodies chemically sensible, with this dif- 
ference only, that the mechanical action of the molecules of zther 
is transmitted to these bodies without chemical decomposition. 
According to their nature, therefore, these phosphorescent sub- 
stances are sensible between certain limits of refrangibility in 
the solar spectrum. 
5th. Besides, if we consider the retina as an organ which per- 
ceives the vibrations of the zther, it is only sensible to rays con- 
tained between certain limits of refrangibility, and the active rays 
_ According to this hypothesis we shall bring back all the effects 
_ produced under the influence of light to the action of one same 
radiation upon different bodies, and there will be as many spectra 
as there are sensible substances. This mode of viewing the sub- 
ject is verified on all the phosphorescent bodies, and on those 
As to the luminous rays, or those which act upon the retina, we 
can only judge of them by our own sensations ; but it is proba- 
ble that the retina of the different beings which exist on the sur- 
face of the globe are not all sensible between the same limits of 
refrangibility. We have some examples of this; amongst others 
of fish which live in the depths of the sea, and which see how to 
ind their way where none of the rays which would be percepti- 
ble to our organs penetrate. 
E. BECQUEREL. 
N.B. M. Arago, after having communicated my memoir to 
he Academy, observed, that in Geethe’s ‘Optics’ a fact was 
elated, the observation of which was due to Seebeck, and which 
is relative to the destruction of phosphorescence by certain rays, 
This natural philosopher has proved that the red rays can extin- 
sh phosphorescence in some bodies which are endowed with 
