M. Plateau's Answer to Objections, 8^c. 439 



same milk left for comparison in the same x'ooni was mouldy, 

 having a strong cheesy smell, and being of course curdled. 



3. Some pieces of meat, unboiled potato, and unboiled cab- 

 bage stalk, were put into water, and into a saturated solution 

 of subcarbonate of soda at the same time, viz. in the beginning 

 of January 1838. It is needless to say, that after a few weeks 

 the animal and vegetable matter put into water began to grow 

 putrescent; the piece of cabbage stalk and potato gradually 

 breaking down and (so to speak) actually dissolving in the li- 

 quid ; whereas those preserved in soda are even at the pre- 

 sent time, April 1839, perfect in shape, and almost as hard as 

 when Jirst put in. It is astonishing that the piece of cabbage 

 stalk should have remained so hard as it is. 



It seems clear from these experiments that subcarbonate of 

 soda prevents tijoo kinds of decay or decomposition to which 

 animal and vegetable matter is subject; first, that kind of 

 decay which is attended with the growth of mould ; and se- 

 condly, that kind of decay which proceeds further, and is 

 synonymous with a complete dissolution of particles. Whether 

 these be but degrees of each other, or be essentially different, 

 we do not now inquire : it is sufficient for our purpose that 

 the decay attended with the growth of mould is very ana- 

 logous to that attended with the growth of fungus, or the rot 

 (dry-rot, as it appears to be called, but perhaps improperly) 

 of wood. It seems hence extremely probable that subcarbo- 

 nate of soda which stops the one, would stop the other ; but 

 to establish this point with certainty, would of course require 

 that experiments should proceed for years in a fungus pit, — 

 as that of Woolwich. Nevertheless, the extreme probability 

 that soda has an anti-dry-rot power must add to its value, 

 though employed solely as an anti-inflammable. 



LXVI. Answer to the Objections published against a general 

 Theory of the Visual Appearances which arise from the Con- 

 templation of Coloured Objects. By J. Plateau, Professor 

 at the University of Ghent. 



[Continued from p. 340, and concluded.] 



OIR David Brewster also has honoured my theory of acci- 

 *^ dental colours, by attacking it (see L. & E. Phil. Mag., 

 May 1834', page 353). I shall here quote the passage. 



" The influence of strong light in rendering the retina par- 

 tially insensible to red rays, even when these rays fall upon 

 a part of the membrane which has not been directly acted 

 upon by the strong light, has been finely shown by the ex- 



