December 2, 1915] 



NATURE 



369 



re than one notebook into his various class- 

 ins, because, provided he is careful to turn 

 r the page when he comes to a new subject, 

 ran take out the loose leaves at his leisure and 

 I them into suitable receptacles. A student 

 : also find as he pursues his study that he 

 uires further information supplementing- his 

 \ ious notes. By writing upon loose leaves he 

 .1 be able to sort the new matter into its proper 

 place. 



Conscientious students are inclined to waste 

 much time in making a fair copy of the notes they 

 have taken at lectures : such copying often 

 becomes mechanical, so that nothing is learnt 

 during the process. The loose-leaf method should 

 make this mechanical work unnecessary, at all 

 e\ ents when the original notes are intelligible. 

 The loose leaves relating to any given subject 

 uld be so arranged as to make reference easy, 

 this purpose the author gives several examples 

 oi classification in which registration letters and 

 numbers are employed. As to the significance to 

 be given to these letters and numbers, we wovild 

 advise the student to consult one of the com- 

 prehensive works of reference, such as, in the 

 case of science, the International Catalogue of 

 Scientific Literature, and to adopt, so far as pos- 

 sible, the plan there set forth. 



An Historical Atlas of Modern Europe from 1789 

 to 1914, with an Historical and Explanatory 

 Text. By C. G. Robertson and J. G. Bartho- 

 lomew. Pp. 24 + 36 maps. (London: Oxford 

 University Press, 1915.) Price 35. 6d. net. 



This is an atlas on new lines, for it deals only 

 with modern Europe, and, except for a few general 

 maps, makes no attempt to illustrate the historical 

 evolution of the British Empire. The size of the 

 atlas is a distinct advantage, as it allows of plates 

 12^x9^ in. Most of the maps are of this size. 

 Central Europe and the Balkan lands are specially 

 well shown, as would be expected, but we miss a 

 separate map of the Iberian peninsula. No doubt, 

 however, the question of expense entailed the 

 omission of the less necessary maps. 



A map of Europe is the only orographical map 

 given. The other maps either show no relief or 

 show it in the old caterpillar fashion. That is 

 disappointing, and certainly lessens the value of 

 the larger-scale maps. There is, of course, a 

 difficulty in showing relief by contours on a map 

 with political colouring, but that might be over- 

 come in many plates by omitting the political 

 colouring and indicating boundaries by red lines. 

 Most of the plates are otherwise admirably exe- 

 cuted, but a few — Russia in Central Asia and the 

 ethnographical map of south-eastern Europe — 

 scarcely come up to the high standard of tech- 

 nique which we expect from the firm of Bartho- 

 lomew. 



The introduction is an excellent commentary on 

 the maps, and keeps the geographical standpoint 

 in view throughout. The atlas is good value for 

 the money and can be highly recommended. 



R. N. R. B. 



NO. 2405, VOL. 96] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



A Question of Albedo. 



The past summer in the Kashmir Valley has been 

 one of extraordinary dryness, with continuous blue 

 skies and hot sunshine. These conditions have ex- 

 tended into the autumn, and during the month of 

 October even the surrounding mountains, so often 

 clouded, have been entirely clear. The snow-line, in- 

 stead of descending to lower elevations with the ad- 

 vance of the season, has steadily risen, until at the 

 date of writing only a few isolated patches of white 

 can be seen on the Pir Panjal range on the south-west 

 side of the valley, and no snow at all on the moun- 

 tains towards the east. It was with a distinct shock 

 of surprise, therefore, that at sunset on the date 

 October 22 we noticed a beautiful dome of snow just 

 topping the eastern mountains, which were still bril- 

 liantly illuminated by the sun. For a few moments 

 the only possible explanation seemed to be that one 

 of the higher peaks of the central Himalayan ranges 

 had made a prodigious upward thrust of several 

 thousands of feet ! However, the earth's rotation 

 movement rapidly transformed this snowfield into the 

 familiar features of the full moon. 



The question I would ask is : Why does the moon 

 appear so white if it is composed of rocks similar in 

 reflecting power to those on the earth? The average 

 albedo of the moon must have been determined, and 

 it is no doubt well known how it compares with Venus 

 or with Jupiter when these are reduced to unit dis- 

 tance from the sun. The rock surface of the moon 

 should reflect far less light than the cloudy surfaces 

 of these planets, and it would be of interest if those 

 who know would explain the apparent whiteness of 

 the moon as seen in daylight. 



A direct comparison of the moon with terrestrial 

 rock surfaces illumined by sunlight is possibly to some 

 extent vitiated by the superposed blue light scattered 

 by the intervening air, which may affect the colour of 

 the moon. Yet it is very difficult to believe that this 

 can convert the greys and browns of rock surfaces 

 into an almost pure white. On several occasions^ in 

 this valley I have compared the waning moon, setting 

 behind the Pir Panjal mountains, and, of course, in 

 full sunlight, with extensive snowfields. These snows 

 are perhaps fifty miles distant, and there Is a con- 

 siderable amount of blue scattered light superposed on 

 the snow, although less than on the moon ; also the 

 light absorbed by the atmosphere is approximately, 

 and mav be exactly, the same for each, if one con- 

 siders the whole path of the light from sun to snow 

 and thence to the observer. When the air is trans- 

 parent enough to see the moon clearly, it appears to 

 me to be distinctly whiter than the snows, which seem 

 dull and yellowish in comparison. 



The daylight colour of the moon suggests, in fact, 

 that Parmenides was right when he considered it to 

 be composed of earthy material mixed with celestial 

 fire, only I should say that the celestial fire greatly 

 predominates ! 



One does not hear much nowadays of the_ glacial 

 theory of the moon's surface, but it would be interest- 

 ing to learn whether the daylight aspect of the moon 

 has been considered by those who believe its surface 

 to be composed of rocks. J. Eversiied. 



Srinagar, Kashmir, November 2. 



