October 14, 1909J 



NA JURE 



47: 



a central metal nucleus surrounded by a viscous layer and 

 an outer shell of rock. On Clairaut's ellipsoidal theory 

 the internal structure is not determinable from outside 

 effects. Observation of the propagation of earthquakes is 

 a direct experiment on the interior ; but even here you 

 cannot go far, because of ignorance of the properties of 

 materials under enormous stresses. The phenomena of 

 terrestrial magnetism are also concerned with the interior. 

 He asked how the weiglit of mountain chains is supported. 

 To avoid crushing, the basal material must have the 

 strength of steel. .\ rival theory is based on the survey 

 of India, viz. that the mass of a mountain is compensated 

 by less dense material underneath ; but Burrard's recent 

 researches show that the defect underneath is not nearly 

 so great as was thought. He pointed out that there was 

 room for a fresh calculation. The presence of a mountain 

 chain supported without collapsing necessitates also that 

 the supporting material shall not have any fluidity at all, 

 or else the mountain chains would gradually settle down. 

 He asked if tlie necessary calculation had been made. He 

 pointed out that Hecker's curve, being of the right shape 

 though of the wrong size, was in conflict with a sup- 

 position of unequal rigidities in different directions. 

 Finally, he propounded a conundrum of Lord Kelvin's : 

 It is possible for any person in this room, if he lived 

 long enough, to turn the earth upside down ! Dr. 

 L. A. Bauer directed attention to the semi-diurnal 

 variation of the earth's magnetism, which has so far not 

 been explained. In reference to VViechert's theory. Prof. 

 Love stated in reply that if it be adopted the rigidities of 

 the supposed metal nucleus and rocky shell required to 

 satisfy the two conditions h — k — i/^ and ^ = 4/15 are re- 

 spectively about three times and about one-tenth the rigidity 

 of steel, .'\ttention was also directed to the scooped-out 

 beds of the ocean as being much more important than 

 mountains. More than half the surface is 2000 fathoms 

 below the sea-level. The earth is not an ellipsoid ; it is 

 the ocean that is so approximately. At the close of the 

 discussion the section again divided. 



In the department of general physics two papers were 

 given by Prof. Poynting : — (1) on the lengthening of loaded 

 wires when twisted ; (2) tlie angular momentum in a 

 beam of polarised light. These have appeared in a recent 

 number of the Royal Society Proceedings. Prof. Frank 

 .Mien followed, dealing with the effect on the persistence 

 of vision of fatiguing the eye with red, orange, and yellow. 

 The persistence is measured by finding the speed at which 

 flickering ceases when a sectored disc is rotated in front 

 of a source, and a curve is drawn representing the whole 

 spectrum. This persistence is measured when the eye has 

 been fatigued with light of definite wave-length. When 

 fatigued with light of 680 /i and 670 /i, only the red part 

 of the curve is affected : fatigued with green only the 

 green part ; but when the fatiguing colour lies between 

 577 iJ. and 650 ;n, the curves differ in both red and green. 

 With wave-length 660 ^ the two curves coincide completely. 

 This means that the fundamental red sensation is at least 

 beyond wave-length 660, and that yellow and orange can- 

 not be simple primary sensations. Prof. Allen also con- 

 tributed a paper on a new method of measuring the 

 luminositv of the spectrum. The principle of the method 

 is that the persistence of a colour sensation is a function 

 of the luminosity only. The next paper was by Profs. 

 E. L. Nichols and E. Merritt, on the effect of low tempera- 

 ture on fluorescence spectra. The measurements consisted 

 in comparing the brightness of the fluorescent spectra of 

 natural wiUemite, commercial anthracene, an alcoholic 

 solution of fluorescein, and one of resorufin at various 

 temperatures from 20° C. to —185° C, these being e.xcited 

 by a quartz-mercury lamp any portion of the spectrum of 

 which, dispersed through quartz, could be focussed upon 

 the fluorescent body. The results were shown by means 

 of curves. In response to a query by Prof. Rutherford, 

 Prof. Nichols stated that the fluorescent bands tend to 

 become narrow as the temnerature is diminished. Sir J. 

 Larmor exoressed his opinion that fluorescence wns due 

 to molecular creeping, but Prof. Nichols replied that 

 though there is hysteresis (thermoluminescence), his e.x- 

 periments were all conducted slowly so as to eliminate it. 

 A paper on an analogous subject, the absorption and 

 fluorescence of canary glac« ."t low temperatures, was con- 



No. 2085, VOL. Si] 



tributed by Mr. R. C. Gibbs. The glass, of known com- 

 position, exhibited a main fluorescence band extending 

 from 048 p. to 059 ji. With decreasing temperature the 

 fluorescence for the most part increases, tlie maximum 

 increase being about 100 per cent. The band, which at 

 ordinary temperature shows a faint indication of two 

 maxima between O'Si fi and 0-535 /*> shows at the lowest 

 temperature ( — 175" C.) two narrow overlapping bands 

 with maxima at 0-514 /i and 0-533 /'■ 



In the cosmical physics department, which was sitting 

 simultaneously. Prof. W. J. Humphreys communicated 

 some results he had obtained from a consideration of 

 European ballons-soiides observations, while Mr. E. Gold 

 presented the report on the present state of our knowledge 

 of the upper air drawn up by Mr. Harwood and himself. 

 One of the most interesting facts was that both Prof. 

 Humphreys and Mr. Gold found that in areas of high 

 pressure (.above 770 mm.) the temperature up to 9-10 km. 

 was greater than in areas of low pressure (below 750 mm.), 

 while at greater heights the conditions became reversed. 

 So long as this condition holds and the isothermal or 

 advective region exists, it appears impossible that there 

 should be anything in the nature of circulatory interchange 

 between cyclones and anticyclones, and the intensity of 

 these systems cannot be maintained. 



Gold and Harwood found remarkable minima in the 

 height at which the advective region begins in March and 

 September, and an attempt was made to connect these 

 minima with the general circulation of the atmosphere. 



On Wednesday, September i, the section again bifur- 

 cated. In the department of cosmical physics Prof. A. L. 

 Rotch gave an account of the highest balloon ascent in 

 America. He found a remarkable result, which occurred 

 in at least two ascents, that the temperature increased in 

 a cumulus cloud in passing from the base upwards. Con- 

 siderable discussion took place, and doubt was expressed 

 as to 'the reality of the phenomenon, but Prof. Rotch 

 stated that the observations were unexceptionable. The 

 fact adds further ditTiculties to the explanation of cloud- 

 formation and its connection with atmospheric motion. 



Dr. Shaw showed photographs of models illustrating 

 the temperature distribution in the free atmosphere over 

 the British Isles in the international week in July, 1908. 

 The models show the gradual production or pushing for- 

 ward of a wedge of cold air at a hei<?ht greater than 

 10 km. The wedge had just reached Limerick on the 

 first day, but two days later extended well over England. 

 It may be noted that the construction of the models was 

 only made possible by the observations obtained near 

 Limerick, in Ireland. 



Mr. Gold read a paper by Mr. A. Harwood on the 

 results of hourly observations with registering balloons, 

 June 2-3, iqoq. At heights above 10 km. there was a 

 diurnal variation of 6° C. to 8° C, with the maximum in 

 the middle of the day, but the values were irregularly dis- 

 tributed, and it was impossible to say how far the varia- 

 tions were real or instrumental. 



Prof. W. J. Humphrevs described an arrangement for 

 obtaining a record of the ultra-violet part of the solar 

 spectrum (below n-2 /j.) at very great altitudps. 



Mr. Stupart read a paper bv F. Nanier Denison on the 

 connection between atmospheric pressure and the motion 

 of the horizontal pendulum of a Milne seismograph. 



.Simultaneously, in the department of general physics, a 

 paper was given by Mr. R. F. F'arhart on the effect of 

 temperature variations on the luminous discharge in gases 

 for low pressures. The potentials were measured which 

 are required to produce, and also those required to main- 

 tain, a luminous discharge for pressures varying from 

 0-2 mm. to ■; mm., and for temperatures from —78° C. 

 to 325° C. Vp to 300° C. Paschen's law holds good for 

 air ; for higher temperatures it does not hold even 

 approximately. Prof. Rutherford considered the paper 

 important, because it raises the whole question as to the 

 d'^nendence of ionisation upon temperature. Prof. H. M. 

 MncDonald sjave the results of his calculations on the 

 diffraction of electric w.aves round spherical obstacles. 

 Prof. Love inauired whether the nropaeation of Marconi 

 waves round the earth could, in the light of these calcu- 

 lations, be attributed simply to the great length of wave 

 employed. Sir J. Larmor reminded the meeting of the 



