ACCIDENTS BY RAIL AND SEA. 179 



apparatus necessitates. Finally, if we state ttiat the apparatus is some- 

 what expensive, and is comparatively difficult to transport, it will suffice, 

 it seems to us, to condemn its use as a method of the first order when it 

 is required to make the examination on a multitude. 



The method of Seebeck causes much loss of time by obliging those 

 examined to classify a large number of colored objects. This is not an 

 easy task for them. It not only progresses very slowly, requiring per- 

 haps an hour, but costs much trouble and evident effort. One may 

 obtain a tolerably clear idea of this by attempting to do the same work 

 with the use of blue-green eyeglasses. The colors are then seen and 

 classified very nearly as they are by the red-blind, and almost the same 

 difficulty is experienced. Seebeck's method, however, is superior to 

 Maxwell's in this, that it requires the subject to make an active use of 

 his chromatic sense, while the other allows him to remain passive, and 

 merely announce his decision. Both methods, however, require too 

 much time to be employed with advantage for the purpose in question. 

 But they are the best methods known to us at present. 



The perimetric exploration with Forster's apparatus may be excellent 

 in more than one case for examining those before examined, but it is 

 not advisable alone and as a primitive method. It is even inapplicable 

 to some persons; it entails much loss of time, requires much exertion on 

 the part of the one examined, and requires an expensive instrument, 

 which is besides very inconvenient for transportation. 



It may be very interesting scientifically to use the spectrum for exam- 

 ining the color-blind ; but this method is not very appropriate for 

 practical purposes ; it requires costly apparatus, and different arrange- 

 ments, which render it more or less long and inconvenient. It does not 

 enter into our plan to give an account here of all the known methods 

 that may be used in the first inspection, or when desired to establish a 

 test for examination. We shall limit ourselves to the examples cited, 

 and to explain in a special chapter the method we have ourselves used, 

 and which of all tried seems to us best adapted to the purpose. 



VI.— NEW PRACTICAL METHOD FOR DISCOVERING AND 

 DETERMINING DEFECTS OF THE CHROMATIC SENSE. 



The method we are going to describe here has been employed in all 

 the examinations of the chromatic sense of the different classes of the 

 population which have been made in Sweden. 



1. — A SHOET SKETCH OF THE GENEEAL PEINCIPLES OP THE METHOD. 



Theoretically, our method most resembles those of Seebeck and Max- 

 well, as it is based upon a comparison between different colors. It there- 

 fore first seeks to discover the chromatic ^ercf/^fio/i of the subject, disre- 

 garding the names he gives to the colors, as generally it is not neces- 

 sary he should designate the names. Our method resembles Seebeck's 



