47 8 



NA TURE 



{Sept. i 3) 1883 



that at marine stations like Bombay, but reaches its n.inimum 

 value in the hottest part of the year, when the ratio at the latter 

 stations is rising towards its maximum. 



When discussing the vapour ten-ion, Prof. Hill remarks that, 

 "while the diurnal variations of vapour tension and atmospheric 

 pressure are connected w ith each other in so far as they are both 

 effects of the diurnal inequality of temperature, it is doubtful 

 whether there is any other connection between them except in an 

 indirect way. At a dry station like Allahabad, where the range 

 of the inequality of vapour tension is less than one fourth of the 

 range of pressure, it could never be supposed that the observed 

 variation of the barometer is caused by the variation of the 

 quantity of aqueous vapour in the air." 



In explaining the afternoon minimum of vapour tension which 

 is so distinctly marked at Allahabad during the dry hot months, 

 a suggestion of Mr. Blanford's is noticed referring it to the 

 semi-diurnal interchange between the lower and upper currents 

 (which is supposed by Dr. Koppen to account for the diurnal in- 

 crease in the velocity of the wind), supplemented perhaps by dif- 

 fusion. The occurrence of a maximum of cloud nearly simul- 

 taneously, lends coun'enance to this view. 



The clouds and rain are found to manifest similar diurnal 

 variations, reaching their maxima nearly (1) when the tempera- 

 ture is lowest ; and (2) when the vapour in the air reaches a 

 maximum, either by diffusion from below or intermixture with 

 the lower strata. 



The heaviest fall recorded in one day during the ten years of 

 observation was I5'48 inches between July 29 and 30, 1875, 

 which has only been approached in the plains by the rainfall at 

 Purneah in Bengal on September 13, 1S79, and the rainfalls on 

 September 17 and 18, 1880, when the disastrous land lip at 

 Naini Tal took place. These abnormal falls are found to be 

 due to the passage of small cyclones (secondaries, as they are 

 generally termed in European weather bureaux) which strike the 

 land on the coast of Orissa, and move northwards along a line 

 separating the westerly winds of Southern India from the 

 easterly winds of the northern plain — the axis as it were of the 

 entire monsoon system. 1 The occurrence of the fall so far west 

 as Naini Tal, together with its exceptional character in 1S80, 

 appears to the writer to have been due to the preponderance in 

 that year of the eastern over the western mon-oon system. 



In regard to wind, Allahabad conforms to the general rule 

 deduced by Dr. Hann for stations near sea-level in every part of 

 the world, viz. that the velocity of the wind in every season is 

 greatest about the hottest hour of the day. 



The double diurnal rotation of the wind, exhibits a peculiarity 

 which is of considerable interest in relation to Mr. Chambers's 

 hypothesis of the connection betw een it and the diurnal varia- 

 tion of the barometric pressure, it is that in the dry hot months, 

 the loop in the diagram representing the nocturnal variation is 

 almost invisible, while in the rainy season it is much more pro- 

 nounced, in correspondence with the nocturnal barometric tide 

 which undergoes similar changes. In the marine climate of 

 Bermuda, as Mr. Chambers has shown, both the nocturnal wind 

 and barometer variations are nearly equal to those which occur 

 during the day, and, in proportion as the climate of Allahabad 

 becomes moister and therefore more maritime, so the variations 

 in these elements appear to approximate in character to those 

 at marine stations. 



Paper XII. "The Meteorology of the North-West Himalaya," 

 by S. A. Hill. — In this paper, which was originally compiled 

 for a gazeteer and afterwards expanded, the author gives one 

 of the most lucid and exhaustive accounts of the meteorology of 

 a single district that we have ever hrd the good fortune to 

 meet with. Not only is the region, one of peculiar interest, 

 owing to the extraordinary facilities it presents for the observa- 

 tion of atmospheric changes, in vertical as well as horizontal 

 range, but the manner in which the data are discussed is so 

 eminently exhaustive, and w ithal attractive, that it virtually forms 

 an almost complete epitome in miniature of meteorological 

 science. In a preliminary description of the climate, and while 

 noticing the great heat of the Punjab and North- West Provinces 

 as compared with regions further south, Prof. Hill alludes to 

 the investigations of Poisson, Meech, and Wiener, as showing 

 that the total heating effect of the sun is a function of the time 

 during which he is above the horizon of a place, as well as his 

 altitude. The region where, according to their calculations, most 



1 Mascart, in his " Mcteorologie arpliquc'e a la Prevision du Temps," hss 

 noticed a similar tendency in Enropean storms to move "vers la region des 

 vents faibles." 



heat falls from May 7 to August 7, lies about latitude 41", and it 

 is to this circumstance, together with the dryness of the air and 

 absence of cloud, that Prof. Hill ascribes the excessively high 

 temperature of June and July in the extreme north of the Pun- 

 jab, and in the plains of Yarkand and Kashgar still farther 

 north. 



In fact (and this is a point which we think has been a good 

 deal overlooked by climatologists) the annual range of tempera- 

 ture, is not merely dependent on the sea distance of a place, but 

 also on its latitude ; the further it is from the equator, cateris 

 paribus, the greater the amount of heat that falls in the -ummer 

 months. On the other hand, since the summer season dimin- 

 ishes in length as the latitude increases, the region where the 

 effect upon the temperature reaches its maximum for the longest 

 period is probably about lat. 254°, where the greatest amount of 

 heat falls from equinox to equinox. 



With respect to the other factor, humidity, the North-Western 

 Himalaya are found to differ very markedly from what may be 

 termed the South-Eastern Himalaya. Thus Darjeeling, though 

 higher, has very nearly the same temperature in January as 

 Simla, Chakrata, or Mussoorie, where the winter rains are more 

 prevalent ; while in May and June, owing to its coming in for a 

 much more copious share of the summer monsoon, it is seven or 

 eight degrees cooler. 1 



The vertical variation in the annual and diurnal ranges of 

 temperature is found to be dependent chiefly on differences in 

 the relative humidity of the air, the ranges being greater at the 

 surface than at 6000 feet, where the lower cloud strata prevail, 

 and greater again at the most elevated stations, where the 

 radiation is excessive. 



Another important element — the vertical decrement of tem- 

 perature — is found to vary considerably in amount and rate at 

 different seasons, being on the whole greater in the summer than 

 in the winter up to 6coo feet. Above this height, especially in 

 the inner ranges, the temperature diminishes very slowly, partly 

 owing to the greater latitude, and partly to the absence of cloud, 

 ard it is to these circumstances, quite as much as to the small 

 amount of precipitation, that the well-known fact of the snow- 

 line being higher on the northern than on the southern side of the 

 Himalaya, must be attributed. After working out the decrements 

 in detail by the help of the method of least squares, Prof. Hill 

 finds that on the mean of the year the temperature diminishes 

 on the mean latitude 32 , at the rate of 2°'S per icoo feet, or 1° 

 in every 357 feet of ascent. In the Eastern Himalaya, it is more 

 rapid, being 1° for 320 feet. 



It is interesting to observe, as Prof. Hill says, that, assuming 

 the rate of decrement to be uniform over the southern slope of 

 the North-West Himalaya, "a mean temperature of 50° Fahr., 

 equal to that of London, would be attained at a height of 9600 

 feet, and the annual range of temperature would probably differ 

 little from that observed in England. The hill sanitaria, at 

 heights of 6000 to 70x0 feet, possess climates comparable as 

 regards temperature to those of Nice, Mentone, and other health 

 resorts on the Riviera," only they appear to be somewhat 

 superior to these in having a much smaller annual temperature 

 range. 



Prof. Hill calculates the height of the perpetual snow-line on 

 the south slope of the North -West Himalaya to be 17,800 feet, 

 which is a good deal higher than the measurements given 

 hitherto. It seems probable, however, that a good many of 

 these, by mistaking glaciers for snow, erred in making it too 

 low. On the inner ranges bordering on Thibet, for reasons 

 already noticed, the snow-line is abcut 2000 feet higher. 



The diurnal variation of pressure — that hitherto unsolved 

 problem for meteorologists — is discussed, though briefly, yet in a 

 masterly manner, and the analogy of the mountain type by vertical 

 exchange of air between their summits and the valleys, to the coast 

 type caused by lateral exchange of air between the sea and the 

 land, is noticed in connection with the corresponding system of 

 mountain winds. 



It is evident, from a perusal of this as well as other facts in 

 connection with the diurnal range, that a complete explanation 

 of it can only be attained by discu-sing data embracing a wide 

 area, in order to eliminate all such local variations of the normal 

 type. 



The annual variation of pressure, is also very well described 

 and explained, and we cordially commend it to the perusal of 

 teachers of physical geography out of text-books, in which the old 



1 This explains why Darjeeling is such a healthy place for children, to 

 whom a high summer temperature is so fatal. 



