180 Mr. Knox on some phenomena of colours , 
were gradually metamorphosed into two others ; one of 
which was formed between the two lower, and the other 
between the two middle slips brought into contact by this new 
arrangement ; this was also proved by the test of the shadow. 
It may be worthy of remark, that in every variety of shape 
assumed by these spectra, the binary characteristic is clearly 
visible in them all. 
Exp. 24. On viewing a set of Newtonian rings, as described 
in Experiment 4, through one of the double slips, while in the 
position fig. 11. pi. IX, the apparatus forming the rings being 
on the table ; a set of narrow binary rings appeared, con- 
centric to the primaries, and near to the edge of the lenses : 
and on lowering the double slip to the second position, 
fig. 13. pi. IX., another set of binary rings appeared in the 
reflected image of the double slip, also concentric to the prima- 
ries, but consisting of broader rings, though less in diameter 
than those of the first set ; and all these three sets were seen 
distinctly, at one and the same time. 
The two sets of binary rings, seen in this experiment, cor- 
respond to the two irregular spectra in experiment 20 ; and 
since the rings must have been formed between the lenses on 
the table ( because no rings are ever formed unless between 
surfaces, one of which at least is spherical), this affords a 
corroborating proof, that the irregular spectra seen in Expe- 
riment 20, although apparently formed in the air, were 
really formed between the two slips of glass lying on the 
table. 
The above results differ so widely from any that have 
hitherto been published, that it is allowable to doubt, whe- 
ther they can be accounted for on the common and received 
