1 16 On the Motion of Camphor towards the Light. 



possible Dr. Draper could sanction such statements in 1844, if, 

 as be says, be bad adopted my theory in 1840 ? 



At page 124 he says that "light which has suffered reflexion 

 at certain angles seems to have undergone a remarkable modifi- 

 cation, being no longer able to put the glass into such a condi- 

 tion that it can cause motion towards the sun." Does this look 

 like settled theory ? 



Nor is the action of metal screens and tinfoil rings in pre- 

 venting a deposit at all explained. At page 126 it is stated that 

 "the ring exerts a kind of protecting action," &c. Again, 

 " This action of a ring formed of good conducting materials 

 might be supposed to arise either from its adding something 

 to the surface of the glass, or taking something away from the 

 glass with which it is in contact ; or it might be imputed to some 

 change impressed on the ray of light," &c. 



The electrical theory noticed in my paper is started at page 

 127. At page 128 it is stated that, if the inner surface of the 

 glass receiver be rubbed with a glass rod, the camphor will 

 deposit itself on the lines traced by the rod. Although the 

 explanation of this fact is perfectly easy *, yet Dr. Draper 

 compares the result with Lichtenberg's electrical figures, and 

 proceeds to ask, " Are we to refer this singular action to the rays 

 of light, to the rays of heat, or to the chemical rays ? " He 

 then proceeds to pass the light through solutions of ammonio- 

 sulphate of copper, bichromate of potash, &c, and obtains what 

 he calls " aphelion camphor deposits." He says, " It does not 

 necessarily follow from the phenomena that any peculiar class 

 of rays is emitted by the sun which bring about this action ; 

 but if there are such, it is a question of interest to find what is 

 the reason that good conductors of electricity render their action 

 nugatory." 



Now is it conceivable that Dr. Draper could have published 

 such statements as these in 1844 if he had had the faintest idea 

 of the true theory ? Or is it conceivable that so industrious and 

 ingenious an experimentalist would not have devised experiments 

 to test his theory had it been the same as mine, and which he 

 now admits to be a sufficient one ? I have looked in vain for 

 any indication of such an attempt. Instead of any settled 

 theory, I find a large number of theories, and a large number of 

 experiments, but nothing is settled. In fact Dr. Draper makes 

 a lottery of a number of theories, and draws out blanks so far as 

 the explanation of the phenomena in question is concerned; 

 and when, twenty years later, another inquirer draws a prize, he 

 claims it as having come from his original lottery. 



* The editorial note in the Philosophical Magazine for 1840, to which 

 Dr. Draper refers, has reference to this fact. 



