It is seen that there is more variation at the red end than at the violet end of the spectrum, and this notwithstanding that the violet rays are more spread out by the prism than the red rays. It is seen that the two eyes are often markedly different. This is not due to inaccuracy of observation, for certain individuals in which this occurred were tested several times with similar results. It is seen that the variations at the red end and the violet end are often independent, and that the absolute length of the visible spectrum differs in different individuals. The following table presents these observations and a few others in another light:-- Table of Maxima and Minima in Wave-lengths, expressed In Millionths of a Millimetre. ------------------------------------------------------------------------- | Violet | Red | |----------------------+----------------------| No. of |Highest| Mean | Lowest|Highest| Mean |Lowest|Individuals |-------+------+-------+-------+-------+------+----------- Women under 30 | 410.0 |402.75| 394.0 | 811 | 772.85| 743 | 17 Men " " | 413.0 |405.0 | 399.0 | 811 | 772.8 | 743 | 17 Women over 30 | 410.5 |406.65| 401.5 | 792 | 767.8 | 743 | 7 Men " " | 407.0 |404.5 | 402.5 | 787 | 773.7 | 758 | 3 ---------------------------------------+--------------------------------- N { right eye | 406 | 687 { left eye | 407 | 717 ------------------------------------------------------------------------- The individual N showed signs of colour-blindness, and is therefore not included in the table, but entered separately. He was unable to recognize the C line of the hydrogen spectrum (wave-length 656), which was brilliantly obvious to the normal eye. These observations[FG] need further confirmation and extension. We intend to continue the investigation each session. They are, however, sufficient to show that in some individuals R. undergoes disruptive change on the impact of light-waves which have no noticeable effect on the retina of other individuals.