206 
Trav^nctlovs of tJie Royal Society of South Africa. 
for Michler's hyclrol in water). The additive property means that the 
sinuous orbit is made up of roughly semicircular portions through which 
the electron passes in turn from one end of the chain to the other, e. g. : 
Fio-. 1. — Michler's hydro!.* 
SO that the total periodic time is the sum of the separate periodic times 
taken in each loop. Also at this stage I may mention that there is not much 
difference between the values of the different tautomerisms, so that 5 loops 
give a wave-length in the middle of the spectrum (A 500 in unloaded mole- 
cules) ; 4 loops give about X 400, viz. yellow substances ; 3 loops give about 
A 300 (colourless substances with photograph able absorption bands); whilst 
substances with less than 3 tautomeric loops, unless very heavily loaded 
with side-groups, are in general colourless, even to the photographic plate. 
It is to be noted that such a sinuous orbit would not be expected to have 
an exact and constant periodic time, but only an average one. This explains 
why absorption -bands are diffuse and not narrow lines as in the case of 
sodium vapour, where the periodic time is constant. The diffuseness of the 
bands means a diffuse periodic time, i. e. a periodic time affected by perturba- 
tions, to use the astronomical analogy. 
It is probable that the path of the electron is not as shown in the 
diagram. Fig. 1, namely passing through carbon atoms, but that the path 
goes in between the successive atoms of the tautomeric chain, making in 
the above case ten sinuosities instead of five (eleven if the particle goes 
round the final atom to continue the orbit in the reverse direction — Fig. 2). 
Fig. 2.— Path of electron. 
The result of my calculations is that (1) the tautomerism 
)C - CH = C( 
has a value of 103 /x/x in wave-length, (2) the tautomerism 
)C - CH = 0 
has a value of 94, and (3) the tautomerism 
)C-CH = NH 
* For clearness, the hydrogens and the non-tautomeric double bonds are omitted, 
