THE DIA TONIC SCALES. 343 



COLOR BLINDNESS. 



Prof. E. L. Nichols, of Richmond, Ky., read a paper on the duration of 

 color impression upon the retinr. The essayist, by a modification of the method 

 of Plateau, had determined for six different portions of the spectrum, the rate of 

 revolution which must be imparted to a disc, with several narrow open sectors, 

 in order to produce an unbroken visual image of the spectral region viewed 

 through the disc. The rate of revolution which may be taken as a measure of 

 persistence of vision was found to be a fraction of the wavy length, and of the 

 intensity of the ray. The results of the experiment described may be represent- 

 ed by a series of curves with wave lengths as apeses and duration of the impres- 

 sion upon the retina as ordinates. These curves show a certain vision fiance to 

 the curves for the relative luminosity of the different spectral regions, as meas- 

 ured by Francis Hofer, Herordt and Hood. The way in which the two curves 

 differ is such as to suggest that these measurements are not efficient to prove that 

 perhaps the duration of impression is inversely proportioned to the luminosity. 

 The difference between the curves was in the higher values for the more refrang- 

 ible rays ; in the curve for the duration of impression. This curve corresponds 

 of necessity to a very faint spectrum. The change which the curve for luminos- 

 ity would undergo, were the intensity of the ray decreased, would, owing to the 

 greater activity of the violet nerves of the eye at less intensities, cause that curve 

 to approach much more nearly, if it did not coincide with, the curve for dura- 

 tion of impression. It was also found that the curve differed greatly in the case 

 of different observers, and to a less degree from time to time for the same eye. 

 The interval of darkness which may be allowed to intervene between exposures 

 of a given duration, without interfering with the apparent continuity of vision, 

 and its variation when the length of exposure raried, was also determined. The 

 exposure varied from 12-1000 second to 786-1000 second, and the interval of 

 darkness was found to vary, but in less degree. 



Prof. Stevens said that the results of Prof. Nichol's investigation were of the 

 greatest importance, as the scientific men of the world who have so long been 

 anxious to form a theory on the question of color blindness have by it been di- 

 rected to a course of investigation which promised to settle the question. 



THE DIATONIC SCALES. 



The next paper was by Dr. P. H. Vander Weyde, on the diatonic scale, ob- 

 tained in the chromatic scales of equal temperament of 12, 19 and 31 tones in 

 the octave,* with exhibition of novel scale indicators and correcting key-board, 

 seemed to be of the greatest interest to the ladies present. The essayist main- 

 tained that in our common tonal system of twelve tones in the octave for the so- 



