Decemkeu 9, 1909] 



NA TURE 



175 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, November 25. — Sir Archibald Geikie, 

 K.C.B., president, in the chair.— Sir W. de W. Abney : 

 The change in hue of spectrum colours by dilution witli 

 white light. The author shows that by diluting the spec- 

 trum colours from the red to the green-blue with moderate 

 percentages of white hght, their hue travels towards the 

 yellow, the change being dependent on the amount of red 

 and green existing in the white added. At a point near 

 \ 5780 the hue remains unaltered by the addition of white, 

 and it is towards this point in the spectrum that the 

 colours on each side of it travel. It is pointed out that this 

 change in hue enables the relative amounts in green and 

 red from k 5000 to \ 6000 to be accurately determined. — 

 Prof. G. E. Hale and F. Ellerman : The nature of the 

 hydrogen flocculi and their structure at different levels in 

 the solar atmosphere. — Prof. H. L. Callendar and H. 

 Moss : The boiling point of sulphur corrected by reference 

 to new observations on the absolute expansion of mercury. 

 — C. Cuthbertson and Maude Cuthbertson : The refrac- 

 tion and dispersion of neon. The refractivities of neon 

 (Ne,) for different wave-lengths are found experimentally 

 to be 



The refractivities of sulphur dioxide for different wave- 

 lengths are found experimentally to be 



6700 

 6500 

 5S00 

 546 [ 

 5000 



(w- 1)106 

 656 '40 

 657'io 

 661 '26 

 663-97 

 66865 



6438 

 5461 

 4SOO 



13402 



13463 



These can be expressed by the formula 



5-133x10'^'^ 

 ;83i7 X 10-' -«'^ 



^-i = - 



where 11 is tlie frequency V/A. Owing to the feebleness of 

 the dispersive power of neon, the accuracy of the value 

 obtained for the dispersion is not to be relied on to less 

 tlian 5 per cent. Revised formula for the refractive indices 

 of helium, argon, krypton, and xenon are given, in the 

 same form, which supersedes the use of Cauchy's formula. 

 — C. Cuthbertson and Maude Cuthbertson : The refrac- 

 tion and dispersion of air, oxygen, nitrogen, and hydrogen, 

 and their relations. The refractivities of these gases for 

 different wave-lengths are found experimentally to be 



(M-i)lo'i 



Cauchy's formula of two terms is shown to be inadequate 

 to express the dispersion of a gas, and a formula of 

 Sellmeier's type is adopted, 



_^_ C 



in this form the refractivities of these gases are given by 

 (he constants shown in the table below. Revised values 

 of the indices of sulphur, phosphorus, and mercury, ex- 

 pressed in the same form, are also given, and it is shown 

 that, on the electronic theory of dispersion, the relative 

 numbers of " dispersion electrons " in hydrogen, oxygen, 

 and nitrogen are as i, 2, and 3 almost e-xactly ; in sulphur 

 and phosphorus, to a less degree of accuracy, as 3 and 4J. 

 In mercury the number is in the neighbourhood of 45 to 5. 



Cxio-a- a„2xio-27 V C/V 



Air 



Hydrogen. 

 Oxygen ... 

 Nitrogen... 

 Sulphur ... 

 Phosphorus 



Mercury ... 



— C. Cuthbertson and Maude Cuthbertson : The refrac- 

 tion and dispersion of sulphur dioxide and hj'drogen 

 sulphide, and their relation to those of their constituents. 



NO. 2093, VOL. 82] 



These can be expressed in a formula of Sellmeier's type, 



_ 5-728 X lo'-^' 

 8929 X io'-^-«-' 



The refractivities of hydrogen sulphide for different wave- 

 lengths are found experimentally to be 



6363 

 5790 

 5461 

 4861 



(m-.)io6 

 636 22 

 641-17 

 644-03 

 65098 



These can be expressed in the same form by 

 4-834 X 10-' 



fi- l~ ^ :p :,• 



7aoa X 10-' - «- 



The number of " dispersion electrons " in SO„ is shown 

 to be approximately equal to the sum of the numbers of 

 " dispersion electrons " in Sj and in 0„. The number of 

 " dispersion electrons " in H.S is, approximately, one more 

 than the sum of the " dispersion electrons " in H, and 

 in S,. — Prof. M. F. Fitzgerald: Flapping flight. — Dr. W. 

 Rosenhain and J. C. W. Humfrey : The crystalline 

 structure of iron at high temperatures. The paper con- 

 tains a preliminary account of observations on the effects 

 of strain on iron at high temperatures. Polished strips of 

 nearly pure iron were heated in vacuo and strained while 

 hot, the central portions of the specimen attaining a 

 temperature of about 1100° C, while the ends remained 

 below visible redness. Heating alone produced a surface 

 pattern caused by a volume change in the metal when 

 passing through the a = transformation, and occasionally 

 where the temperature was highest a slight tarnish which 

 revealed the 7 crystals. Heating and straining in vacuo 

 showed that at all temperatures attained deformation took 

 place by means of slip on the gliding planes of the crystals ; 

 three distinct regions could, however, be distinguished, and 

 temperature estimations by the method of Joly's meldo- 

 meter agree with the identification of these regions with 

 the a, /3, and 7 ranges of Roberts-Austen. This identifica- 

 tion is supported by differential heating and cooling curves 

 given in the paper. In the a range the number and 

 intensity of slip-bands increases rapidly with increasing 

 temperature ; at the transition point — which is seen as a 

 well-defined line across the specimen — the bands suddenly 

 cease and remain minute during the range ; in the 

 7 range the bands are again numerous, but differ from 

 those observed in the a range by their straightness and 

 regularity and by the frequent occurrence of twin crystals. 

 These observations are illustrated by three photomicro- 

 graphs. The authors consider that their observations 

 strongly support the allotropic theory of Roberts-Austen, 

 particularly since they show that iron, although at a 

 higher temperature, is markedly harder and stronger than 

 a iron. So much is this the case that when such a speci- 

 men was broken while hot, the fracture took place in the 

 region of hottest a iron, just before the transition point. 

 The present observations also demonstrate the similarity 

 of 7 iron, as found in nearly pure iron when heated, with 

 the well-known " 7 iron " found in alloy steels. — Dr. 

 .A. E. H. Tutton : The relation of thallium to the alkali 

 metals : a study of thallium-zinc sulphate and selenate. 

 This communication contains the results of an investigation 

 of the thallium salts of the zinc group of the monoclinic 



.series K.2M I 5, O4 L.6H.O, analogous to the previous in- 

 vestigation of the simple rhombic salts of the series 

 R2 s ^*- '^he conclusions formed as the result of the 

 latter research are fully confirmed and independently sub- 

 stantiated, as regards the relations of thallium to the alkali 



