G. W. Howes— Iron in Dolerytes from New Hampshire. 33 



saw that this was due to an optical illusion, for his hair 

 appeared of a bright purplish-red hue. The singular appear- 

 ance lasted perhaps a couple of seconds, when his hair resumed 

 its natural color, which was white. This observation corresponds 

 with that made by Tait. 



I give now an instance, where chronic effects of a similar 

 character were noticed by me for a couple of weeks continuously, 

 during convalescence from typhoid fever. In this case white 

 objects appeared of a not very intense orange-yellow hue, the 

 general effect on a landscape beinc; such as is produced by the 

 orange-yellow rays of the setting sun. Here the activity of the 

 green and violet nerves was diminished relatively to that of the 

 red. The auditory nerve was also evidently allected during 

 the same period, but precisely in what wav 1 did not ascertain. 



It is a matter of yearly observation with me, that effects, 

 similar in kind wit li those first noticed, are produced by pro- 

 longed exposure to bright white light out of doors. Under 

 such circumstances white objects no longer appear pare white, 

 but are tinted plainly purplish-red, and rather dull greens 

 assume a gray hue, as though all the green in them had been 

 neutralized, while strong greens are considerably reduced in 

 intensitv (saturation.) Upon leaving the blinding glare and 

 entering a darkened room, it often for several seconds appears 



Two of these cases and, probably that of Tait, point out, that 

 our apparatus for the reception of waves of light of medium 

 length, is more liable to be over-strained by nervous shocks or 

 by "prolonged excitation, than is the case with those designed 

 for the reception of waves of greater or lesser length. Nervous 

 derangement and prolonged excitation, are then causes, which 

 may produce temporary green color-blindness. 



Art. IV.— On grains of Metallic Iron in Dolerytes from New 

 Hampshire; by George W. Hawes. 



The presence of metallic iron in certain basalts and dolerytes 

 has been repeatedly proved. It was first shown by Dr. 

 Andrews that it was contained in the basalts of the Giant's 

 Causeway* Eeuss has proved its presence in Bohemian 

 bas ilta : and in this country it has been found in the Mesozoic 

 dolerytes of New Jersey by Cook.f 



In all these cases the iron has been detected by a microchem- 



ical method. If a portion of a rock is pulverized, and the 



*F 



tc 



