RECENT ADVANCES IN SCIENCE 365 



colour-blindness, and increasing with the person's perception 

 of colour. By means of a specially designed spectrometer each 

 observer was made to divide the spectrum into a number of 

 " patches," such that each patch appeared to him or her to be 

 of one colour. The more perfect the perception of colour, the 

 greater the number of patches, and this number constituted 

 the observer's " mark." The " mark " was as high as 26 for 

 one student and as low as 5 for two. The results were graphed 

 in the usual " frequency-curve " way, " marks " being plotted 

 along a line as abscissal, the ordinates being the number of 

 observers with the corresponding mark. The important point 

 now arises as to whether we get a frequency-curve of the usual 

 type with one maximum, or not. If so then colour-blindness 

 corresponds merely to an outlying portion of the main curve, 

 near to the origin. But if the curve shows, say, two peaks, 

 a main one over say the mark 20 and a smaller but still definite 

 maximum over say 10, with a decided minimum between the 

 two peaks, say over 12, it would seem that the colour-blind 

 are a definite class by themselves with a definite maximum of 

 their own. This latter result would correspond with the 

 Young-Helmholtz theory, the main class with their large 

 maximum at, say, 20, being " trichromats," the smaller class 

 with their maximum at 10 being the " dichromats," or persons 

 not possessing one of the three nerve sets of the Young-Helmholtz 

 theory. Dr. Houstoun's results certainly show enough of the 

 biometrician's " scatter " to hazard the guess that colour- 

 blindness is merely an outlying portion of normal colour-vision. 

 If this is so the result would be hard to reconcile with the 

 Young-Helmholtz theory. But it is clear from the results 

 that many more observers than 80 are required to disprove 

 the existence of separate maxima for the trichromats and 

 dichromats, and perhaps even for monochromats. 



A paper in the May number of the Physical Review, by 

 Q. Majorana of Turin, discusses the possibility of testing by 

 direct experiment the validity of the second postulate of the 

 Relativity hypothesis, viz. that an observer who measures 

 the velocity of light finds the value the same whether both he 

 and the source are relatively at rest or whether either he or the 

 source both are in uniform motion. The author makes use of 

 a device in which a number of vertical mirrors are mounted on 

 the periphery of a horizontal brass wheel. By means of these 



