August 1, 1902.] 



SCIENCE. 



175 



effects on a Klemencie receiver, the length 

 of which was varied. The curves bring 

 out the existence .of two upper partial 

 vibrations or overtones; in some cases the 

 third overtone also appears. The wave- 

 length of the fundamental was later meas- 

 ured by the interferometer method. Fur- 

 ther work on the same subject is in 

 progress. 



Some Experimenis on Retinal Fatigue and 



Persistence of Vision: Frank Allen, 



Cornell University. 



The experiments Avere a continuation of 

 some discussed in the Physical Review, 

 Vol. XI., 1900, p. 257. It is a matter of 

 common observation that when a person is 

 some time in the dark the retina suffers 

 'adaptation,' which enables faint light to 

 be more readily perceived. Some experi- 

 ments were performed by the Nichols 

 method of the measurement of the persist- 

 ence of vision, to see how adaptation pro- 

 gressed with time. A normal measure- 

 ment of the persistence of vision was made 

 with the eye in its ordinary condition of 

 adaptation for diffused daylight. Measure- 

 ments were made after darkness adaptation 

 of one-, three-, five-, ten- and fifteen-minute 

 intervals. The results, when plotted with 

 time intervals as abscissas and increases of 

 persistence of vision as ordinates, give a 

 curve much like a mag'netic saturation 

 curve. The measurements for fifteen min- 

 utes are practically the same as for five 

 with all colors. Adaptation seems to be 

 quite complete in five minutes. Longer in- 

 tervals than fifteen minutes were not tried. 



Experiments were next made in the same 

 way by fatiguing the eye with light of 

 various wave-lengths. Observations were 

 made on the same wave-lengths as the 

 fatiguing colors. The zero of reference 

 was the normal persistence of vision with 

 different colors; 'saturation' curves were 

 obtained exactly as described above, the 



maximum fatigue being realized in three 

 minutes with all colors. 



The maxima of the curves differ, how- 

 ever. For wave-length .675/-/- the maxi- 

 mum is represented by 14. For yellow 

 (.589/-i) fatiguing has no effect. For green 

 (.523/^) the maximiim is 10. For blue 

 (ATOfi) no change of persistence occurs un- 

 der the fatiguing stimulus of even ten 

 minutes' exposure to the blue of an arc 

 spectrum. In the violet (.430/-^) the maxi- 

 mum is 20. These maxima, when plotted 

 with wave-lengths as abscissas, give three 

 elevations corresponding suggestively with 

 red, green and violet. 



The persistence of vision on the temporal 

 side of the retina, ten and twenty degrees 

 distant from the center, was measured. 

 Throughout the spectrum the persistence 

 diminished the further out the measure- 

 ments were made. Some peculiarities were 

 noticed in the part of the curve correspond- 

 ing to the yellow region of the spectrum, 

 connected doubtless with the 'yellow spot.' 



The complete paper will appear in the 

 Physical Review. 



A Radiometric Receiver for Electric 

 Waves: G. F. Hull, Dartmouth College. 

 The form of receiver for electric waves 

 generally used in quantitative work is the 

 Klemencie thermoelement. Here the dis- 

 sipation of the energy into heat at the eon- 

 tact of two wires joining the two halves of 

 the resonator gives rise to an electromotive 

 force which causes a deflection of the gal- 

 vanometer. In the form of receiver de- 

 scribed in this paper this heat is made 

 evident by the radiometric action on a very 

 small vane of a torsion balance. Among 

 the various receivers used the one so far 

 giving the best results consists of two sil- 

 vered strips of mica of the proper length 

 for the Avaves used. These are divided at 

 their centers by a very fine diamond 

 scratch and are mounted vertically with 



