February i6, 1905J 



NA TURE 



m 



versely as the radius if the density is constant, the pressure 

 will balance the pull on a spherical absorbing particle of 

 the density of the farth if its diameter is about a hundred- 

 thousandth of an inch. The possible effects of radiation- 

 pressure may be illustrated without going to such fineness 

 as this. In the case of a particle of the density of the earth, 

 and a thousandth of an inch in diameter, going round the sun 

 at the earth's distance, there are two effects due to the sun's 

 radiation. In the first place, the radiation-push is i/ioo of 

 the gravitation-pull, and the result is equivalent to a diminu- 

 tion in the sun's mass. In the second place, the radiation 

 absorbed by the particle and given out again on all sides is 

 crushed up in front as the particle moves forward and is 

 opened out behind. There is thus a slightly greater pressure 

 on the advancing hemisphere than on the receding one, and 

 this appears as a small resisting force in the direction of 

 motion. Through this the particle tends to move in a de- 

 creasing orbit, spiralling in towards the sun. As there is 

 good reason to believe that some comets, at least, are com- 

 pesed of clouds of dust, there is hope that some of their 

 eccentricities may be explained by the existence of radiation 

 pressure. If the particles of a dust cloud circling round the 

 sun are of different sizes or densities, the radiation acceler- 

 ations on them will differ. The larger particles will be less 

 affected than the smaller, will travel faster round a given 

 orbit, and w\\\ draw more slowly in towards the sun. Thus 

 a comet of particles of mixed sizes will gradually be de- 

 gr.ided into a diffused trail lengthening and broadening, the 

 finer dust on the inner and the coarser on the outer edge. 

 If a planet, while still radiating much energy on its own 

 account, captures and attaches to itself, as a satellite, a 

 cometary cloud of dust in which there are several different 

 gr.'ides, with gaps In the scale of size, it may be possible that 

 in course of time the radiation-pressure effects will form the 

 different grades into different rings surrounding the planet. 

 Such may possibly be the origin of the rings of Saturn. 



GEOGRAPHICAL RESULTS OF THE THiET 

 MISSION. 



"T^llE paper read by Sir Frank Younghusband at the Royal 

 Geographical Society on Monday, P'ebruary 13, was 

 one of the most interesting and instructive that the fellows of 

 thai society have been privileged to listen to for many years. 

 It afforded a striking exemplification of the advantages of 

 a due coordination of geographical facts and their com- 

 bination, by a master-hand, into a well-arranged whole. The 

 country traversed by the Tibet mission was by no means a 

 terra incognita to the geographer, for its main features had 

 long been known through the labours of the zealous native 

 explorers of the .Survey of India. But it is none the less 

 true that Sir I-'rank Vounghu.sband's admirable descriptions 

 of the conditions of nature and man in that romantic region 

 enabled his audience to realise those conditions in a way that 

 was never before possible, and brushed away many false 

 ideas which had been previously entertained. The speaker 

 was also able to touch briefly upon some of the results ob- 

 tained by the scientific experts who accompanied the mission, 

 as well as by the survey party under Captains Kawling and 

 Kyder. which in the late autumn did excellent work along 

 the whole course of the L pper Brahmaputra, proving de- 

 finitely that no peaks higher than Everest exist on this flank 

 of the Himalayas. 



In regard to the general nature of the country traversed. 

 Sir F. ^'ounghusband was able to correct the current idea 

 that the whole of Tibet is more or less barren and worthless. 

 This may be true for northern Tibet, the part traversed by 

 recent European explorers, but not for the southern third, 

 which is dotted over with thriving villages and well-built 

 residences. The valleys in which Lhasa, Gyantse, and 

 Shigatse are situated, as well as that of the Brahmaputra, 

 are neither barren plateaux nor narrow, V-shaped 

 gorges, but flat valleys covered with good soil, well 

 irrigated, and richly cultivated. The passage to Tibet, as 

 made by the Kongra-lama Pass, involves, however, a sudden 

 change from the deep-cut valleys and luxuriant vegetation 

 of Sikkim to wide plains on which not a tree is to be seen, 

 while if, in some secluded nook, a plant a foot high is met 



NO. 1842, VOL. 71] 



with it is a curiosity. The summer climate of Khamba- 

 jong was described as charming, while the unrivalled pano- 

 rama of the Himalayas, at the very culminating point of 

 their grandeur, is a full compensation for anything that may 

 be otherwise lacking. Sir Frank Younghusband 's eloquent 

 descriptions of the snowy range as seen from the north, with 

 the ever-varying atmospheric effects, are of special interest as 

 the first ever given by a European capable of appreciating 

 adequately the glories of the prospect. 



The discovery by Mr. Hayden, of the Indian Geological 

 Survey, of a bed of fossil oysters, permitted an accurate de- 

 termination of the age of the hills in this part of Tibet, show- 

 ing them to be geologically quite recent, though somewhat 

 older than the main axis of the Himalayan range. The 

 ("humbi \'alley, through which the final advance was made, 

 is less wide and open than the valleys in Tibet proper, of 

 which, in fact, it is not considered a part. The passage 

 hence into Tibet, made during the height of winter by the 

 Tang-la Pass, 15,200 feet high, involved much suffering from 

 the effects of the great cold (18° below zero F'ahr.) combined 

 with the rarity of the air. The subsequent march over the ele- 

 vated plateau was made in the teeth of bitter winds and 

 blinding blizzards, which continued through January, 

 February, and -March. But on arrival at Gyantse (.April 11) 

 the pier 'iig cold was left behind. Willow and poplar trees 

 were bursting into foliage, and the banks of the river were 

 covered with masses of iris-plants, which later on became 

 sheets of purple. On July 14, the day of the start for Lhasa, 

 heavy rain destroyed the delusion that Tibet is a rainless 

 country. Frequent rain was experienced until September, and 

 the size of the rivers showed that this part of Tibet receives 

 — probably up the Brahmaputra Valley — a quite considerable 

 rainfall. Finally, in a lovely valley covered with trees, rich 

 with cultivation, and watered by a river as broad as the 

 Thames at Westminster, the mysterious city which no living 

 European had seen before was at last reached, hidden away 

 by range after range of snowy mountains. It proved any- 

 thing but a dreamland city, and its streets were horribly 

 muddy, but the grand lama's palace was an imposing, mas- 

 sive structure. Even the leading men were of low mental 

 calibre, having much of the nature of children. The Ti 

 Rimpochi — the leading lama — though benevolent and 

 genial, had few intellectual attainments, and was firmly con- 

 vinced that the earth was triangular ; while the religion of 

 the Tibetans was described as the most degraded form of 

 Buddhism in existence. 



THE LONDON CONFERENCE ON SCHOOL 

 HVGLENE. 



T^HE conference on school hygiene, organised by the 

 ■*- Royal Sanitary Institute, met on February 8, 9, and 10 

 at the University of London. Sir .Xrthur Riicker, who was 

 installed as president of the conference, delivered an address 

 in which he insisted that the elements of education should 

 include some knowledge of the dangers by which mankind is 

 surrounded and of the means to keep them at bay, and that 

 those to whom voung lives are entrusted should learn the 

 main outlines of hygiene. 



The ignorance of household management and of the prin- 

 ciples of hygiene among the poor is responsible in no small 

 measure for their high preventable mortality, their inferior 

 physique, their intemperance and their poverty. How pos- 

 sible it is to better the conditions of modern life, and thus to 

 improve the health, happiness, and physical powers of the 

 people, and thereby their mental vigour and industrial 

 efficiencv, is generally recognised, and to this end a suitable 

 hygienic education, moral and material, of the future parents 

 seems essential. Not only have 15,000 medical men and the 

 Commissions on Physical Degeneration recommended that 

 such teaching should be made compulsory, but the English 

 Board of Education and the Scotch Education Department 

 have accepted that recommendation. It is important that 

 from the earliest years of school life children should be taught 

 by example as well as precept the elements of healthy living. 

 The knowledge that may be procured subsequent to that age 

 is often gained at the price of a needlessly costly personal ex- 

 perience. The object, then, of school hygiene is to secure for 



