132 COLOR-BLINDNESS IN ITS KELATION TO 



veuted us from publishing this worii before the reform was introduced. 

 If this fact should render the publication of these labors less indispeu- 

 sable for the time being, we must not forget the importance and neces- 

 sity of directions which will serve in the future for our own railways, as 

 well as for the introduction of a similar reform elsewhere. 



The importance of uniformity in the method of examination, in the 

 classification, and in the principles relating to the disposal of the jjer- 

 sonnel, cannot be too highly estimated, for this is of consequence, not 

 only to science, and especially to statistics, but also to a purely practical 

 end. This fact becomes the more forcible when connected with the in- 

 vestigation of the sense of color among seamen ; for every reform of this 

 kind within the province of navigation naturally assumes an interna- 

 tional character. Our classification as well as our method of examining 

 the color-blind is founded upon the Young-Helmholtz theory, and wo 

 cannot refrain from enumerating here the principal elements. This 

 theory is assuredly not the only one, nor even the last that has been 

 given to the public and gained partisans ; but it is, in our opinion, the 

 best for the end in view, and it will be seen that it essentially responds, 

 as far as regards practical interest, to all that we have a right to require 

 of a theory. We have no intention of attempting to establish its correct- 

 ness. We make use of it for a definite purpose, under the conviction 

 that it is a needful basis for the systematic and accurate solution of 

 some of the practical questions under consideration. 



In brief, the object of this work is to give a practical and clear idea 

 of the nature of color-blindness, of its importance to marine and railway 

 service, and, finally, a concise summary of the principles to be followed 

 and the measures to be taken in order to secure immunity from its pecu- 

 liar dangers. The reason why we confine ourselves almost exclusively 

 to railways here is that the reform in view has already been introduced 

 iuto this department, and a valuable experience acquired. And it is 

 clear that these results may equally well be applied to navigation, at 

 least in all essentials. 



Color-blindness in many other departments of practical life also leads 

 to serious inconveniences, and as it is desirable that an examination of 

 the chromatic sense be undertaken on a large scale in schools, as a guide 

 in the choice of professions, we hope this memoir may serve in a meas- 

 ure to this end. We should, moreover, be very happy to have the 

 opportunity (so rarely accorded to physiology) of being useful to human- 

 ity, without the intervention of practical medicine. 



I.— HISTORICAL SKETCH. 



Color-blindness has been known for a long time, and, therefore, has 

 its history. The first cases known to the public are mentioned in a let- 

 ter from Joseph Huddart* to Joseph Priestley, dated January 15, 1777, 



* An Account of persons who could not distinguish colors. By Mr. Joseph Hnddait, 

 in a letter to the Rev. Joseph Priestley, L.L.D., F.R.S. Philosophical Transactions of 

 the Royal Society of Loudon. Vol. Ixvii. For the year 1777, part i, p. 260. 



