198 Mr. M. Donovan on the supposed Identity of the Agent 



On the fourth day the yellow ring had risen to a pale pink of 

 the first order, and the outer ring was negative, as on the pre- 

 ceding day. 



On the fifth day the pink ring had increased in intensity, and 

 the other structures remained the same as before. 



On the sixth day the pink had risen to a very bright blue. The 

 diameter of the lens was now 0*867 of an inch, and its thickness 

 0733, being an increase of 0233 of an inch in thickness. 



On the seventh day the capsule burst, and upon removing it 

 and the soft pulp which formed about one-tenth of an inch of 

 the outer margin of the lens, the pink ring, with the white band 

 both within and without it, and the black mass at the centre of 

 the rectangular cross, were as distinct as ever. Hence it is ma- 

 nifest that the rise of the tint from yellow was not the effect of 

 any expansive pressure produced by the swelling of the lens and 

 the reaction of the capsule. 



The descent of the tint from bright blue to pink was no doubt 

 owing to the polarizing action of the extended capsule being 

 withdrawn. In order to prove this, I took the capsule, which is 

 a tough and elastic membrane, and having stretched it, I found 

 that it polarized, just before it tore, a white of the first order. 

 Now the value of this tint is nearly equal to the difference be- 

 tween the values of the pink and blue of the second order of 

 colours. 



The preceding results throw much light on the physiology of 

 the crystalline lens ; and I shall have occasion, in a separate 

 paper, to point out the conclusions to which they lead respecting 

 the cause and cure of cataract. 



Allerly by Melrose, 

 May 6, 1837- 



XXXI. On the supposed Identity of the Agent concerned in the 

 Phenomena of ordinary Electricity, Voltaic Electricity, Electro- 

 magnetism, Magneto-electricity, and Thermo-electricity. By 

 M. Donovan, Esq., M.R.I.A. 



[Continued from p. 127.] 

 Section II. 



FULLY aware that a conviction of the identity of the agent 

 in all the phenomena called electric is firmly established 

 in the minds of the scientific, and that experiments of apparently 

 so convincing a nature have been brought to bear upon the sub- 

 ject that doubts seem to be no longer entertained, I scarcely 

 know how to declare, in terms that shall protect me from the 

 imputation of presumption, that I have never been able to view 

 the matter in the same light. It is my duty to assign reasons for 



