( 746 ) 
other colour than green appearing in photo-chemical decomposition 
is to be attributed to a subhaloid poorer in halogen. 
If this subhaloid actually existed, it would have to have, in analogy 
with the other silver subhaloids, a maximum sensitiveness to light 
in the infra-red in accordance with its absorption spectrum. It would 
then have to make its influence strongly felt in spectrum photography, 
if the silver haloid plate previously received an exposure below its 
liminal value. H. Leymann *°) in his experiments as to the infra-red 
spectra of alkali metals has actually observed that through a previous 
exposure and an ammonia bath a highly sensitive silver bromide 
gelatine plate increases its sensitiveness via A into the infra-red 
near FRAUNHOFER's line Z, but, and this is the great point, a conspicuous 
rise of sensitiveness in the infra-red appears nowhere from his expe- 
riments. Consequently what H. LEHMANN observed was nothing else 
than the well-known auto-sensitation of the plate. So we may say 
that a subhaloid richer in halogen than the a-sublaloid does not exist. 
According to Nierski’s rule silver haloid would have to take the 
place of the colourless subhaloid assumed above, but it shows the 
deviation that the maximum of its absorption spectrum is not situated 
in the infra-red, but in the blue or violet, i.e. where the number 
of vibrations is about twice as high. Consequently in the case of 
silver haloid, too, the cause of the sensitiveness to light is to be relegated 
to electro-magnetic light resonance. 
In the synthesis of silver haloid from silver and balogen, through 
the series of subhaloids, the electro-magnetic resonator undergoes 
changes which show a striking resemblance to the foliowing well 
known phenomenon in aconstics. If we take a small, thin bar with 
a fixed and a detached end, it will resound at a tone corresponding 
to its key-note; by constantly lengthening this bar, the key-note is 
lowered, and the resonance will set in at a lower number of vibra- 
tions, until, after it has reached its maximum length, the next leng- 
thening will at the same time fix the detached end, by which the 
key-note will get one octave higher, and accordingly the resonance 
will set in at the double number of vibrations. 
Nietski’s rule points to a yellowish green subhaloid as a subhaloid 
still poorer in halogen than the yellow one. In numerous experiments 
repeated under various circumstances, by endeavouring to keep D 
low and constant, I have not been able to observe a trace of it. 
It is true, the appearance of the mixed colours of the subhaloids 
poorest in halogen points to the formation of a yellow subhaloid as 
the last one formed photo-chemically. Consequently the formula 
Agon Hal, may be assigned to it. 
