340 Mr Herschel on certain Deviations from Newton's Scale . 
The curve constructed from this Table, as in the case of the 
apophyllites, is given in Fig. 6. 
The rings in this crystal, when crossed by a plate of sulphate 
of lime, are affected in the same way as those in carbonate of 
lime, tourmaline, &c. and the axis is therefore of a repulsive cha- 
racter. 
The facts above adduced suffice to shew that vast differences 
exist in the scale of action, which a single axis may exercise on 
the differently coloured rays, and that, whether we regard the 
single apparent axis of any of the above crystals as the resultant 
of two others equal to it in energy, but of an opposite character, 
situated at right angles to it and to each other, with Dr Brewster, 
or as being itself the real axis of polarization. For the resultant 
axis being the same for all the colours, the partial actions of 
each of the supposed axes on the former hypothesis, having the 
same point of compensation for all the colours, must be equal to 
each other and to the resultant force for them all. The mere 
fact, therefore, of a deviation from Newton’s scale, however enor- 
mous in the tints of any regular crystal with one axis, cannot be 
regarded as affording of itself any argument for the substitution 
of two others for it in that particular substance, because each of 
such axes acting separately, would exhibit a scale of tints perfect- 
ly identical with that of the axis whose place they supply, and 
therefore, by parity of reasoning, should be regarded as the re- 
sultant of two others, and so on, ad infinitum. This reasoning 
appears to me conclusive against any analogy between crystals 
with one and two axes, founded on a deviation of tints in the 
rings of the former. But I cannot help regarding the pheno- 
mena I have described as affording considerable support to the 
very ingenious theory of the philosopher just mentioned, as 
applied to crystals with two axes, inasmuch as they establish the 
existence of that diversity in the scales of action of the simple or 
elementary axes, without which their points of compensation (or 
the poles of the lemniscates they exhibit in polarized light) must 
of necessity be coincident for all the simple colours, a coincidence 
which, as has been already remarked at the beginning of this 
paper, seldom or never takes place. This I conceive to be the 
view which Dr Brewster himself has taken of the phenomena of 
the deviation in crystals with two axes, and to afford ocular 
