186 PROFESSOR WARTMANN ON DALTONISM, 
the same at first to the naked eye, will become manifestly distin- 
guished by the use of the transparent screen. This method ap- 
pears to have been practised for the first time by Prof. Seebeck, 
the father, towards the year 1817*. Nothing can equal the sur- 
prise of a daltonian when the errors which he commits every 
day in the appreciation of colours are thus disclosed to him. 
Unhappily the tint of the coloured glasses and their number 
cannot be prescribed in advance ; the impossibility of a rigorous 
classification of the innumerable varieties of daltonism obliges 
us to choose them @ posteriori for each particular case. We 
may add, that their employment only remedies mistakes in the 
specific nature of colours, and leaves in general those which apply 
to the shades of one and the same tint. 
Vi 
RECAPITULATION. 
In recapitulation, I have sought to establish the following 
facts :— 
1. That daltonism was not investigated by the ancients. 
2. That among the moderns it has only been authentically 
proved in individuals of the white race. 
3. That there exists a very considerable number of varieties 
of it, from those persons who only perceive two colours, or rather 
two sensations,—the one of brightness, the other of obscurity,— 
to those who even by candle-light confound only colours which 
closely approximate, such as shades of blue and green of equal 
intensity. 
4, That there are many more daltonians than is generally 
supposed, 
5. That the female sex furnishes a very small proportion. 
6. That they can, in certain cases, be recognised by some ex- 
ternal signs. 
7. That there are as many with blue as with black eyes. 
8. That daltonism is not always hereditary. 
9. That it does not always affect all the male members of the 
same family. 
10. That it does not always date from the birth. 
11. That daltonians do not judge of complementary colours 
as we do. 
* Seebeck. Mem. cit. p. 216. 
