570 



NATURE 



[July i, 1920 



where there is no other development of the mineral, 

 was considered. Most of these veins are regarded as 

 having been formed shortly after the nodular deposits. 

 The fibres grew upwards and downwards from a plane 

 in the marl, and were probably deposited by descend- 

 ing solutions, being' precipitated at planes of tension 

 in a contracting medium. The veins of fibrous 

 calcium carbonate of "beef" described by Dr. Lang 

 show similar structure and field relations, and doubt- 

 less originated under similar conditions. — W. A. 

 Richardson ; A new model rotating-stage petrological 

 microscope. This instrument is intended as a sub- 

 stitute for the larger pre-war models, which at the 

 present time could be manufactured only at very high 

 prices. It is provided with a mechanical stage inter- 

 changeable with a plane stage and a conventional sub- 

 stage, and provision is made for rapid change from 

 parallel to convergent polarised light. Owing to the 

 reduction in size, a rotation of 270° only can be pro- 

 vided for the rotating stage. — W. Barlow : Models 

 illustrating- the atomic arrangement in potassium 

 chloride, ammonium chloride, and tartaric acid. In 

 the case of the chlorides the suggested structure recon- 

 ciles the X-ray phenomena with the crystaUine sym- 

 metry. The arranf^ement proposed for tartaric acid 

 agrees with the graphical formula of the chemists, and 

 the molecular groups have the symmetry and relative 

 dimensions of the crystals. 



Royal Meteorological Society, June 16.— Mr. R. H. 

 Hooker, president, in the chair. — W. H. Dines : The 

 ether differential radiometer. This instrument has 

 been designed to measure the radiation from the sky 

 after sunset. It consists of two glass test-tubes 

 containing air and a few drops of ether con-- 

 nected by a glass U-shaped tube containing ether to 

 serve as a pressure-gauge. Each test-tube is pro- 

 vided with a movable shield, which protects it from 

 draughts and allows radiation from one direction only 

 to fall upon it. It is used by first directing radiation 

 from the sky upon one of the test-tubes, and then 

 radiation from a "black" body at a known tempera- 

 ture. The known temperature is adjusted until the 

 change has no effect upon the pressure-gauge, and 

 when this is the case it may be assumed that the 

 radiant energy absorbed by the test-tube from the 

 sky is the same as that from the black bodv, whence 

 the radiation from the sky is found by a table. The 

 equivalent radiation temperature of the sky is often 

 below 0° F., and a method is shown by which in 

 this case the sk^- radiation can be found without the 

 use of freezing mixtures. This is done bv com- 

 pensating the small radiation from the sky'bv the 

 excess of radiation from a hot body, so that neutral 

 effect is obtained. The method of calculation and of 

 making up the results is given. — Prof. S. Chapman 

 and E. .\. Milne : The cornposition, ionisation, and 

 viscosity of the atmosphere at g-reat heights. In' the 

 stratosphere, owing to the absence of large-scale 

 mixing, the different constituents of the atmosphere 

 must tend to separate out by diffusion, so that the 

 composition varies with the height : in particular, 

 well-known calculations have shown that, on the usual 

 assumption of the presence of free hvdrogen, the 

 atmospl^ere above i-o km. must consist filmost en- 

 tirely of hydrogen. The authors criticise this assump- 

 tion ; an evamination of the evidence renders uncertain 

 the actual existence of this hvdrojjen atmosphere, 

 and the authors accordini?ly recalculate the variation 

 of composition with height on the assumption that 

 hvdroe^en is absent. In this rase helium, the next 

 lightest element, is the predominating constituent 

 above too km. Thp rpsults are then used to make 

 an estimate of the depth to which o-. ^-, or 7-radia- 

 tion arriving from an extra-terrestrial source would 



NO. 2644, VOL. 105] 



penetrate the atmosphere. It appears that the range 

 of a-particles would extend down to about 80 km., 

 some 20 km. below the auroral zone. In the case of 

 /3- and 7-racliation it is found that the maximum 

 absorption, and consequently the maximum ionisation, 

 should occur at heights of about 50 km. and 25 km. 

 respectively. In each case the region of appreciable 

 ionisation would be confined to a layer of 35 km. 

 thickness, and the unexpected result emerges that the 

 layers would be comparatively sharply defined at their 

 under-surfaces, which practically "coincide with the 

 positions of the maxima. These estimates have an 

 interesting bearing on recent theories of the existence 

 of ionised layers in the atmosphere. Lastly, attention 

 is directed to the fact that at great heights, though 

 the coefficient of viscosity is little altered, the density 

 is so small that the effective viscosity is very high, 

 so that any large-scale motion must die down 

 immediately. 



Royal Microscopical Society, June 16. — Mr. A. N. 

 Disney, vice-president, in the chair. — L. T. Hogben : 

 The problem of synapsis. The data of Mendelian 

 experiment furnish the only critical basis for cor- 

 relating genetic phenomena and cell-structure, and 

 recent work on the cytoplasmic inclusions (Duesbcrg, 

 Gatenby, and others] indicates that these elements 

 fulfil none of the conditions which would provide a 

 satisfactory material foundation for alternating, and 

 in many cases biparental, inheritance of any sort. 

 The theory of synapsis postulates the conjugation in 

 the meiotic phase of homologous chromosomes derived 

 from alternate parents preparatory to their segregation 

 in the reduction division, and thus affords an inter- 

 pretation of gametic purity and allelomorphism. The 

 theory itself rests upon the assumption of the per- 

 sistent individuality of chromosomes and the definitive 

 organisation of the nuclear reticulum. The study of 

 the meiotic phase raises three questions : (a) Is there 

 an actual conjugation of chromosomes in the pro- 

 phase? (/?) If so, in what manner is it effected? 

 (y) Do the chromosomes which pair in synapsis 

 separate in the reducing divisions? As regards the 

 first, it is pointed out that the parasynaptic and telo- 

 synaptic interpretations for animals are mutually 

 exclusive ; the early meiotic phenomena in plants and 

 animals are probably very different. With respect to 

 the second, the question of discovering a mechanism 

 for the interpretation of partial linkage arises. To the 

 last question it is impossible to provide a definite 

 answer from the available data, hence the most valu- 

 able evidence on synapsis is inferred from the different 

 sizes and shapes of chromosome pairs in premeiotic 

 mitoses. It is submitted, therefore, that while the 

 cytological phenomena of hybridisation and mutation 

 may vield sig^nificant facts, a clear recognition of the 

 relation of the mitotic chromosomes to the organisa- 

 tion of the interkinetic reticulum and a fuller kn--." 

 ledge of the synaptic processes are the most pressing 

 needs for further development of the chromosome 

 hypothesis.— Sir Horace Darwin and W. G. Collins: 

 .V universal microtome. This instrument, which is 

 designed on similar general principles to the Cam- 

 bridge rocking microtome, cuts sections from objects 

 embedded in paraffin or celloidin or from frozen pre- 

 parations. It has the advantage over the rocking 

 microtome of cuttinp^ flat sections. The plane of the 

 sections is horizontal, which facilitates examination, 

 and the orientating object-holder is of a novel form 

 and easv of adjustment. The rigiditv of the frame and 

 object-holder, and the fact that the knife is rigidiv 

 clamped at both ends, secures uniformity in the sec- 

 tions. The microtome has no large working surfaces 

 which must be covered with oil. hence irregularities 

 due to yarving thickness of the oil-film are eliminated. 



