116 Prof. Kelland’s Supplementary Remarks on certain 
chromic vision, which seem so puzzling when related, cease to 
be matter of any surprise *. 
[To be continued.] 
XVIII. Supplementary Remarks relative to certain Arguments 
against the Theory of Molecular Action according to New- 
ton’s Law. By the Rev. P.Keviann, M.2A., F.RSS.L.S E., 
F.C.P.S.,8¢., Professor of Mathematics in the University of 
Edinburgh, late Fellow and Tutor of Queen’s College, Cam- 
bridge. 
BENG called upon by Mr. Earnshaw in the Number of 
the Philosophical Magazine for December (S. 3. vol. xxi, 
p- 444.) to reply directly to a series of categorical questions, 
and being at the same time desirous of keeping the discussion 
as simple and disentangled as possible, I trust 1 may be allowed 
the benefit of an early insertion of the following remarks, as 
proper to precede anything which either party may add to the 
controversy. I believe we are all agreed in desiring that this 
point should be cleared up asa preliminary step. I will there- 
fore, for the present, confine myself exclusively to it. The 
matter in question resolves itself into the answers to the fol- 
lowing queries. 
1. Does it follow from the hypothesis which I have adopted 
that the three following expressions are equal,— 
2.>, (or +“ 208) sin? a) 
2% (¢ r +*"2y°) sin? “8 
2% (¢ , +423 #) sin? “28, 
they being the proportions of force to disturbance, parallel re- 
spectively to 2, y,andz? On the assumption of their equality 
depend the arguments adduced at pp. 341 and 343 of the Philo- 
sophical Magazine for November, by my respective opponents. 
* The late celebrated optician Mr. Troughton, who was a remarkable 
instance of this sort of vision, informed me that he could not distinguish the 
scarlet coats of a regiment of soldiers from the green turf on which they were 
drawn up, nor ripe cherries from the leaves of the tree which bore them. 
His eyes, however, were perfectly sensible to rays of every refrangibility as 
light, but the spectrum afforded him only the sensations of two colours, 
which he termed blue and yellow; pure red and pure yellow rays exciting 
in his mind the same sensation. [See a paper by the late Mr. G, Harvey 
on an anomalous case of vision, reprinted from the Transactions of the Royal 
Society of Edinburgh, in Phil. Mag., 8. 1. vol. Ixviii, p, 205.—Epiz.] 
