390 



SCIENCE 



[N. S. Vol. LIV. No. 1399 



principal object of tlie study was to find the effect 

 on flicker of various " wave-forms " of light dis- 

 tribution throughout the intermittent cycle. Rota- 

 ting discs were used, cut to various simple shapes 

 and openings, and rotated in such relation to a light 

 BOurc« that the illumination of the observing target 

 could be interrupted gradually, abruptly, partially, 

 or for varied fractions of the total cycle or period 

 of intermittence. The speeds were found at which 

 the sensation of flicker disappeared (" critical 

 speeds ")• These vary in a systematic manner with 

 the change of wave-form, but in a different manner 

 from their course at high intensities. A strikingly 

 simple mathematical expression has been found to 

 represent the critical speed-wave-form data. If the 

 wave-form is represented by its expansion in a 

 Fourier series, the critical speed is directly propor- 

 tional to the logarithm of the coefGlcient of the first 

 periodic term of the expansion, divided by the aver- 

 age value. 



The effect of tension on the electrical resistance 

 of some of the more unusual metals : P. W. Bridg- 

 MAN. In this investigation those metals have been 

 examined which are abnormal in that their electrical 

 resistance increases under hydrostatic pressure. It 

 is normal for the resistance of a metal to increase 

 under tension. The poiat at issue was whether the 

 metals which are abnormal in their pressure coeffi- 

 cients would also be abnormal in their tension coeffi- 

 cients. Five metals are known whose pressure 

 coefficients of resistance are abnormal; these are 

 bismuth antimony, lithium, calcium, and strontium. 

 It was found in this investigation that the tension 

 coefficients of only two of these, namely bismuth 

 and strontium, are abnormal, whereas that of the 

 other three are normal in that the resistance in- 

 creases under tension. Taken in conjunction with 

 the view of the nature of metallic resistance which 

 I have developed recently elsewhere, these facts are 

 taken to indicate that the mechanism of conduction 

 in lithium is by a passage of electrons between the 

 atoms, whereas in bismuth the conduction is mainly 

 by the passage of electrons through the atoms. In 

 strontium it is probable that both types of conduc- 

 tion are present, in calciimi that the conduction is 

 mainly of the first type, and in antimony mainly of 

 the second. The alloys manganin and ' ' therlo, ' ' 

 whose pressure coefficients are abnormal, have also 

 been investigated, and their tension coefficients 

 found to be normal. This is also in accord with the 

 theory. 



The conductivity of mixtures of nitrogen and 

 chlorine in a flaming arc: W. A. Notes. For about 



seven years the author of the paper and his assist- 

 ants have attempted to secure the direct combina- 

 tion of nitrogen and chlorine by methods similar 

 to those which are used in the preparation of the 

 oxides of nitrogen by the use of the electric dis- 

 charge. Some of the early experiments seem to 

 indicate that nitrogen and chlorine combine in the 

 electric arc, but after a very careful elimination of 

 every trace of oxygen and of moisture from the 

 apparatus no combination could be established. 

 Less than 0.3 of a milligram of combined nitrogen 

 was found in an experiment which was conducted 

 for 51 hours. When air was subjected to the same 

 conditions several grams of the combined nitrogen 

 were obtained. 



Bose Atoll, Samoa, in its relation to recent change 

 in sea level: Alfred G. Mayor. This rarely visited 

 atoll proves to be composed of lithothamnion rather 

 than coral. The atoU rim was once about 8 feet 

 higher than at present, and has been cut down 

 nearly to present sea level after the ocean subsided 

 to this extent in recent times. The extreme isolation 

 of the atoll is shown by the fact that there are only 

 three species of plants upon the island; a Pisonia 

 forming a beautiful grove of trees, a small yellow- 

 flowered Fortulaca, and a creeping pink-flowered 

 Boerhaavea. A rat allied to a Malayan form, and 

 widely distributed over Polynesia is the only 

 mammal on the island. It is interesting to see that 

 all the islands of American Samoa indicate that the 

 sea was once at least 8 feet higher than at present, 

 and Eose Atoll leads us to infer that the climate 

 was tropical when the sea level was highest, for 

 fossil corals and lithothamnion are found in the 

 atoU rim above present sea level. 



- ' ' Turtle Oreodon Layer " or " Bed Layer, ' ' a 

 contribution to the stratigraphy of the White Biver 

 oligocene {results of the Princeton University 19S0 

 expedition to South Dakota: W. J. Sinclair. This 

 paper describes the lowest member of the Oreodon 

 beds in the Big Badlands of South Dakota, a 

 pinkish gray clay with several zones of rusty no- 

 dules at its top. Although it has supplied abundant 

 fossil bones to collectors for over seventy years, 

 very little has been published about it, and the 

 present paper endeavors to give some details re- 

 garding its nature, the origin of the sediments, con- 

 ditions under which they were laid down and so on, 

 and to tie up certain of the changes both in sedi- 

 ments and faunas to a climatic factor. The first 

 fresh-water algal limestones to be identified in any 

 of our continental tertiary formations are described. 



