514 MEMOIR OF GEORGE WILSON. 



read before the Boyal Society of Edinburgh. From the fre- 

 quency of this defect, Dr. Wilson perceived the danger attending 

 the use of red and green signals on railways, and of the red and 

 green lamps on the port and starboard sides of our^naval and mer- 

 cantile steam- vessels, and of the use of the same colours in light- 

 houses. He brought the matter before the notice of the Royal 

 Scottish Society of Arts, and the attention of the railway 

 companies was seriously drawn to the necessity of examining 

 their engine-drivers as to their ability to distinguish the coloured 

 signals. The whole of his observations on this subject were 

 published as a separate work, entitled ' Researches on Colour 

 Blindness.' l 



Another of Dr. Wilson's important investigations was " On the 

 action of dry gases on organic colouring matters, and its relation 

 to the theory of bleaching," 2 from which, after experimenting 

 with various gases and solvents, both in darkness and sunlight, 

 he drew the conclusion, that "chlorine can bleach though 

 oxygen be absent ; neither water nor any other liquid is essen- 

 tial to the decolorising action of chlorine, otherwise than as 

 enabling the gas and the colour to come within the sphere of 

 chemical action, by dissolving both. A similar conclusion, 

 mutatis mutandis, may be extended to oxygen, sulphurous acid, 

 hydrosulphuric acid, and hydrochloric acid, but with this quali- 

 fication, that specific differences may be expected to occur with 

 all the gases named, as to their action on any one colouring 

 matter, and with different colouring matters as to their depoit- 

 ment with any one of the gases." 



Beside these researches, Dr. Wilson attempted to decide the 

 question of the decomposition of water into its constituent gases 

 by heat alone, by analyzing the bubbles that rise when the red- 

 hot drop of oxide that is produced during the combustion of 

 iron in oxygen falls into water ; but this neither confirmed nor 

 disproved the views of Professor Grove. 3 He read communica- 

 tions also before the Eoyal Society of Edinburgh, " On Dr. Wol- 

 laston's argument from the limitation of the atmosphere as to 



1 Sutherland & Knox, Edinburgh. 



2 'Trans. R.S.E.,' vol. xvi. part iv. 



3 ' Quarterly Journal of Chemical Society.' 1847. 



