350 



NA TURL 



[August io, 1905 



ment basin has been calculated from a map on the scale 

 I : 4,000,000 for the Sudan and Uganda, and from one of 

 I : 2,000,000 for Egypt. The area of catchment of the 

 Nile basin is 2,867,600 square kilometres (1,107,227 square 

 miles). The area of the basin will vary according to the 

 distance to which its limits are considered to extend on 

 the west of the Nile northwards of Khartum. Captain 

 Lyons has taken it as far as the cliff of the desert plateau, 

 or the first marked rise of the desert where the cliff is 

 absent, probably, on the average, about 3 to 4 kilo- 

 melres (2 to 25 miles) from the edge of the cultivation. 

 The whole of the Nile basin below Khartum, and prac- 

 tically all the White Nile basin, are non-effective in 

 increasing the river supph", since the occasional local 

 cloud-bursts mav be neglected. The Bahr el Ghazal, as 

 has been shown by recent measurements of the volume 

 discharged, is also practically non-effective. 



Mr. S. Tkisu T.\mur.\ has contributed to the Monthly 

 Weather Rcviexv (Februarv. and April) two papers dealing 

 with applications of the Fourier methods of anaivsis, one 

 to ice formation and the other to the nocturnal cooling 

 of the ;ttniosphero. 



.V \"1;kv compact form of direct-reading cvmometer for 

 the measurement of wave-lengths and frequencies in con- 

 nection with electric-wave telegraphy is described by Prof. 

 J. A. Fleming in vol. xix. of the Proceedings of the 

 Physical Society of London. In the described form the 

 cymometer can be used to measure not only the length of 

 the outgoing wave from a sending aerial, but also the 

 length of the wave being received. The instrument can 

 further be used for measuring the capacitv of a Leyden 

 jar or tlie inductance of a circuit for high-frequency 

 currents. 



In the Journal de Physique for May, M. Adricn Gu^b- 

 hard contributes a paper on photographic action, illustrated 

 by curves showing the darkening due to development as 

 a function of the time, and the superficial changes as a 

 function of the sum of the causes producing them — as he 

 calls it, the " photographic function." It is well known 

 that the effect of greatly over-e.\posing a negative is to 

 reverse the photographic action, sometimes producing a 

 ■positive instead of negative impression. M. Gu^bhard 

 discusses the theory that the photographic function, after 

 reaching its maximum and descending to a minimum, 

 attains a second maximum, followed by a second mini- 

 mum, and he describes experiments in support of this 

 view. 



Prok. O. Z-Wotti Bi.\nco, of Turin, has published 

 (Florence : L. .S. Olschki, 1905) a short discussion on 

 Dante's " Ouaestio de .Aqua et Terra " considered in the 

 light of modern geodesy. The question as proposed by 

 Dante was essentially whether the water of the terrestrial 

 globe is anywhere higher than the land which emerges 

 from it. This question resolves itself largely into what 

 is the definition of height adopted. According to Dante's 

 belief that the earth was a sphere, points would be at 

 the same height if they were equally distant from the 

 centre, and the fact that the earth is not spherical, but 

 ellipsoidal, would thus afford, in effect, an answer to 

 Dante's question according to which the sea-level is 

 considerably higher at the equator than at the poles. This 

 particular interpretation appears to be the one favoured 

 by Prof. Bianco. 



No. 2q of the monograph supplements of the Psycho- 

 logical Review contains the first part of a new series 

 of "Yale Psychological Studies," edited by Prof. Charles 

 NO. 1867, ^'Ol-. 72] 



H. Judd, a large part of which is devoted to a series of 

 studies of eve movements in connection with optical 

 illusions. The contributors are Messrs. C. H. Judd, 

 Cloyd N. Macalister, \V. M. Steele, E. H. Cameron, and 

 Henry C. Courten. Some idea of the researches on eye 

 movements may be obtained from the following necessarily 

 fragmentarv summary. In order to trace the movements 

 of the eye during the fixation of different points in the 

 visual field, a tiny speck of Chinese while was attached 

 to the cornea, and kinematographs were taken showing 

 its movements as the subject followed the various details 

 of a diagram. This was applied in the case of several 

 well known optical illusions in which the lines of figures 

 appear distorted or equal lengths appear unequal. In 

 another series of experiments the subject was made to 

 record his impressions by a series of pin pricks. 



In the Bulletin de I'Academie Iloyale de Belgique. 

 No. 5, p. 21)1, Prof. \V. Spring describes experiments which 

 he has niade on the limit of visibility of fluorescence. A 

 conical beam of light of great intensity was brought to a 

 focus in solutions of fluorescein of gradually increasing 

 dilution. Fluorescence was perceptible on an area equal 

 to one square millimetre at the apex of the conical beam, 

 when the solution contained ixio-'* gram of fluorescein, 

 but imperceptible when the solution was ten times more 

 dilute. On the assumption that in the limiting fluorescent 

 condition at least one molecule of fluorescein is present 

 in each cubic centimetre of solution, the value 1x10-'^ 

 gram is calculated as the superior limit of the weight of a 

 molecule of fluorescein, and 2.5x10--' gram as that of 

 the weight of an atom of hydrogen. 



So.ME interesting observations on the decomposition of 

 silver oxide at high temperatures are recorded by Mr. 

 G. N. Lewis in the current number of the Zeitschrift fiir 

 fhysilialische Chemie (vol. lii. p. 310). The velocity of 

 decomposition of the oxide, when heated at 330° C. to 

 350° C, is at first so small that no appreciable evolution 

 of oxygen is observed during several hours. The rate of 

 change increases rapidly, however, as decomposition pro- 

 ceeds, passes through a maximum, and then gradual!} 

 falls to zero. Experiments carried out to elucidate the 

 peculiar phenomenon indicate that the reaction is autc- 

 catalytic, the silver produced by the decomposition being 

 the catalytic agent. Other substances, such as platinum 

 black and manganese dioxide, are found to exert a similar 

 influence on the rate of decomposition of silver oxide. 



.•\ CONTINUOUS series of articles on the radio-activity of 

 the soil and of the atmosphere is being written for I.c 

 Radium by Prof. Geitel. These articles connect tcgether 

 the several original papers published by Prof. Geitel in 

 conjunction with J. Elster, many of which have already 

 received notice in these columns. The number of l.e 

 Radium for July 15 contains in addition an article on the 

 results obtained by the use of radium in the treatment 

 of cutaneous cancer. It is illustrated by some striking 

 photographs. 



In a brief note in the current number of the .l((i del 

 l.inc'i Prof. .-\. Righi states that, using an experimental 

 method essentially different from that employed by Prof. 

 McClelland, he has obtained results which fully confirm 

 the connection maintained by the latter to exist between 

 the atomic weight of a substance and the amount of 

 secondary radiation which it emits when subjected to the 

 ^ and 7 rays of radium (compare Nature, vol. Ixxi., p. 

 543, and Ixxii., p. 158). The method used was to measure 

 the change of potential of a dioc of the material suspended 



