ACCIDENTS BY EAIL AND SEA. 171 



they wonld be forced to distinguish and jadge the night-signals alone 

 by the intensity of the light. 



The result of all that we have just said is, it seems to us, that the 

 proposed change of the signal colors is not very practical, and such 

 would be the case with any other choice of two colors. It must at least be 

 conceded that the new signal colors would be to every normal observer 

 worse than those now in use with us, as with nearly all nations; in 

 brief, if they were adopted, it would diminish the public safety. We 

 must add that, by adopting them, the principle we have explained 

 is not taken into consideration, according to which it is necessary to 

 use a system of signals adapted to all kinds of color-blindness, since 

 the violet-blind are not able to distinguish between yellow and blue. 

 The proposed change should therefore be rejected, it seems to us, on 

 every iiractical consideration. 



{h) Colorless liglit and darJcness, black and white. — It has been seen 

 that it is impossible to hope for colored signals suiting every one, 

 color-blind or not ; it becomes necessary, therefore, to try to devise a 

 plan for establishing a system of signals independent of colors, and 

 based upon the introduction of a colorless light of different degrees of 

 intensity. While there is nothing more sensible to our sight than the 

 relative intensity of two lights placed side by side (when the absolute 

 intensity does not exceed certain limits), in the present case the 

 only comparison involved is made from memory, so to speak, which 

 is equivalent almost to an appreciation of the absolute intensity 

 of light. We are so far from being able to judge of this, that, in spite 

 of a deeply felt need and constant efforts, science even has not suc- 

 ceeded in discovering suitable measures to apply to it. 



It is, however, necessary to acknowledge here that a system of signals 

 based only on two extremes of intensity of light, namely, on light and 

 darkness, white and black, ought to suit the normal observer as well as 

 the color-blind. Moreover, such a system ought to satisfy all exigencies, 

 ])rovided it is practically applied, and that two signals only are sufficient. 

 A white and black flag, etc., would fully suffice during the day ; but 

 such would unfortunately not be the case at night, for a black light is 

 a contradiction of terms, and it would be necessary, consequently, ac- 

 cording to this system for the night, when signals are of the greatest 

 importance, to be limited not to three, but to one signal only, unless the 

 absence of all signals could bo considered as one. Here it might be 

 well asked, whether the better system is not that which is based on the 

 alternations of darkness and light, that is, movable signals or echpsed 

 signal-lights. As far as we know, no system has yet been discovered, 

 based upon the principles alluded to above, which could advantageously 

 take the place of the one actually in use. 



(c) Form, movement, number. — If we do not succeed in finding a suit- 

 able system of signals, based on the differences of the quality and quan- 

 tity of light, there remains but to appeal to some arrangement in space, 



