178 



NATURE 



[August ii, 1910 



idea of the difficulties encountered by this route may 

 be gathered from the author's experiences. Were it 

 possible to construct a railway from Ichang, at the 

 lower entrance of the Yangtse gorges, through to 

 Vunnan-fu, produce would readily find markets at the 

 treaty ports on the lower river. In 1872 the present 

 writer ascended the gorges, and concluded from his 

 survey that it would be impossible to utilise this sec- 

 tion of the river for steam navigation. The late Mr. 

 .Archibald Little appeared to have confirmed this view 

 when he made his memorable ascent in 1887. 



The story of this journey is admirably told, and 

 rendered all the more attractive by a series of well- 

 chosen photographs. J- T. 



DOES THE INDIAN CLIMATE CHANGE?' 



ANYONE who has examined carefully the meteor- 

 ological elements of any country, whether they 

 deal with pressure or rainfall, will have noticed that 

 tlie curves formed by plotting the values for conse- 

 cutive winter or summer seasons, or even for whole 

 years, present a very wavy appearance. A closer 

 inspection of such curves brings out the fact that 

 they are really of a composite nature, and are made 

 up by the superposition of waves of long and short 

 lengths. , . , 



Such curves indicate that the meteorological 

 elements not only oscillate, about a mean value, 

 rapidly and to a considerable extent in magnitude, in 

 a short period of time of about three or four years, 

 but that, in addition to these variations, there is 

 another oscillation, or perhaps several others, occur- 

 ring over very much longer periods. 



It is the presence of the long oscillations which 

 has given rise to the idea that climates are per- 

 manently changing. This is due to the fact that in 

 many cases meteorological observations made in a 

 homogeneous manner do not extend over a sufficiently 

 long period of time to exhibit a complete wave or 

 oscillation, and the conclusion of climate change_ is 

 drawn incorrectly from the portion of the wave which 

 is indicated. 



The main difficulty met with in dealing with a 

 long series of observations is that those made in the 

 early days are not so accurate as those made more 

 recently with modern instruments and methods. 

 Thus while the data may show a change in the 

 meteorological elements, such a variation may be 

 purely fictitious, and due to either the instruments, 

 the methods, the observers, or a combination of all 

 three. 



In the volume under notice attention is directed 

 to the fact that since the year 1894 the monsoon in 

 north-west India has indicated a very marked weak- 

 ness, and the suggestion has been made that a per- 

 manent change in the climate of that region has 

 taken place, due, as some believe, to increased irriga- 

 tion or diminution in forests. 



The question of the strength of the monsoons in 

 India is of such great importance to the inhabitants 

 of that country — for it means drought or plenty, 

 according as the monsoon is weak or strong — that Dr. 

 Walker, the director-general of Indian observatories, 

 discusses the subject in considerable detail in this 

 memoir. In the first portion of this work he de- 

 scribes the care he has taken to use only data, ex- 

 tending over a great number of years, which can 

 be thoroughly trusted, the records being obtained 

 from the same stations throughout the whole period 



Memoirs -of the Indian Meteorological Department, vol. xxi.,_ part _i. 

 "On the Nleteorological Evidence for supposed Changes of Climate in 

 India," By Dr. Gilbert T. Walker, F.R.S. (Simla, 1910.) 



NO. 2128, VOL. 84] 



of time considered. Each province is separately dealt 

 with, and the rainfall tabulations and curves begin 

 at the earliest year possible and end at 1908. 



Without entering into the results from each area, 

 the broad conclusions need here alone be summarised. 

 Thus Dr. Walker states that 



" although there is no proof of any permanent climatic 

 change, there has been a tendency over a large part of 

 north-west and central India for rainfall during the past 

 thirty years (a) to increase to a maximum between 1892 

 and 1894; (6) to sink to a minimum in 1889; and (c) to 

 improve slowly since that time. Over the remainder of 

 India there do not appear to have been any progressive 

 changes of importance." 



Dr. Walker, in seeking the causes of this variation, 

 remarks, in the first instance, that (a) and (6) nega- 

 tive any explanation which has irrigation as a basis, 

 and that as the destruction of the forests on a large 

 scale ceased about twenty years ago, the expected 

 improvement in the rainfall during the last fifteen 

 or twenty years does not agree with the actual facts. 



Failing local causes for variation, he shows that 

 the true explanation is to be found in the extra- 

 Indian area. Thus he finds that in the Nile there 

 was a rise to a maximum in 1892 to 1894, followed 

 by a rapid fall to 1899, from which time until 1906 

 a deficiency has prevailed, while in 1908 a very great 

 improvement occurred. 



This comparison shows the close association be- 

 tween the monsoon rainfall and the height of the 

 Nile, and suggests that they are both dependent on 

 the Arabian Sea current. 



He, however, goes still further afield, and utilises, 

 in a practical manner, some of the results of the 

 investigations which have been made in recent years 

 at the Solar Physics Observatory, South Kensington. 

 In the researches just mentioned, it was demonstrated 

 that when in any year the pressure over South 

 America was in excess, that over India was deficient, 

 and vice versa. As low pressure over India means a 

 good monsoon, and high pressure a weak monsoon, 

 the close meteorological relationship between these 

 two very distant countries becomes of great import- 

 ance. 



Dr. Walker states : — 



" Further, it is an established fact that the monsoon 

 rainfall in India tends to be abundant when pressure is 

 high in the Argentine Republic and Chili, and low in the 

 Indian Ocean : it shows a fairly close correspondence, there- 

 fore, with the excess of pressure in South America above 

 the pressure at Mauritius." 



Using the data for these countries, he shows that 

 the favourable character of the extra-Indian condi- 

 tions rose to a maximum in 1892, fell to a minimum 

 in 1899, and has on the whole recovered since that 

 time. Thus he writes : — 



" There are valid reasons, therefore, for regarding these 

 extra-Indian conditions as having largely determined the 

 general character of the Indian rains." 



The discussion of the question as to whether the 

 climate of India changes leads him finally to the 

 following inferences : — 



(a) " The recent deficiency of monsoon rainfall in a 

 large part of central and north-western India must be 

 attributed to something abnormal in the larger movements 

 of the atmosphere and not to human agency in India ; 

 (b) the deficiency has not lasted long enough to justify 

 the conclusion that there has been a permanent change of 

 climate ; and (c) there are marked indications of a return 

 to good seasons." 



WlLU.tM J. S. LOCKVER. 



