Jan. :?T, 1875] 



NA TURE 



229 



change of elements tnay take place ; this, however, of 

 course depends upon the amount of change which the 

 actual mean motion may undergo, from the successive 

 smaller perturbations of the next thirty years. 



BORREI.LV'.S CoJlET OF Decehber 6.~Thu5 far it 

 does not appear that any orbit of the last comet dis- 

 covered at Marseilles has been published. The following 

 elernents, founded on observations between Dec. 7 and 

 26, received from M. Stephan, Director of that Obser- 

 vatory, may therefore possess some interest : — PeriheUon 

 passage, Oct. 79, 1S74, at ih. 36m. Greenwich time ; 

 ascending node, 282° 12' 49' ; distance of periheHon 

 from node, counted on the orbit in the direction of 

 motion, 15'' 23' 34" ; inclination, So° 56' 28" ; distance in 

 perihelion, 0'49565 ; motion, retrograde. These ele- 

 ments bear no close resemblance to those of any pre- 

 viously computed comet. 



ON A PROBABLE CAUSE OF THE CHANGE 

 OF THE COURSE OF THE AMU DARYA 

 FROM THE CASPIAN TO THE ARAL* 



r F the central regions'of Asia are really, as is surmised, the 

 •*■ localities where the youth of the human race was passed, 

 agriculture, aided by irrigation, has probably been practised 

 from the earliest ages on the banks of the Oxus. 



The description, in Herodotus, of the plain in Asia through 

 which a mighty river called Aces ran and watered the lands of 

 five nations inhabiting its banks, may possibly not apply to the 

 Oxus valley, though the Chorasmians are specified as one of the 

 five nations. But the passage clearly describes the distribution 

 of the waters of the Aces for the purposes of cultivation, and it 

 may with reason be inferred that the art of irrigation was in 

 vogue in the Kharesmian oasis some two thousand years ago. 

 However this may be, the Chinese traveller Hiouen-thsang 

 speaks of Khiva, in the seventh cenfury of our era, as forming 

 but a narrow band on both banks of the Oxus ; a description 

 which does not admit of a doubt that the waters of the river were 

 then employed in watering the land. 



At the present d.ay the Khanate of Khiva, as is well known, 

 owes its fertility to the numerous canals of irrigation derived 

 from the Amii, between Pitnak and Nukus. The heads of these 

 artificial canals are kept open during the part of the year included 

 between the months of May and November, and thus allow the 

 summer or flood waters of the river, which pass into them, to 

 be distributed over the land of the Khanate. As the volumes 

 and velocities of the streams entering the several canals are less 

 than that of the flood of the Amii, a deposition of silt, carried 

 in suspension by the waters, takes place in these canals. For 

 this, among other reasons, their heads are closed during the 

 winter and early spring months, so as to allow of their running 

 dry, and the deposited silt being then cleared, by manual labour, 

 from their beds. 



I am not aware that even a rough estimate has ever been 

 made of the quantity of water thus diverted from the Amii, and 

 passing into these canals, during the period of the yearly floods. 

 It is clear, however, that the physical phenomena of the river 

 must be sensibly affected by the abstraction of so large a body 

 of water from its stream, and I will, therefore, make some 

 attempt to arrive at an approximation to the truth on this head, 

 though the data at my disposition are insufficient, and the condi- 

 tions of the problem are such as render it difiicult to attain to 

 any great precision. 



The land under cultivation in the Khanate is generally esti- 

 mated at about two millions of acres ; if we assunie that the 

 Tyhole of this cultivation requires the constant use of water, about 

 40,000 cubic feet per second must be taken by the several canals 

 from the river. It is perhaps true that many of the crops do 

 not require more than partial irrigation, but, on the other hand, 

 the population of about 400,000 souls, and the cattle of the 

 Khanate, are entirely dependent on the river for their water 

 supply. The excess, therefore, assigned for irrigation may be 

 considered as absorbed by the people and by the cattle, and the 

 estimate of 40,000 cubic feet per second maybe allowed to stand 

 for the present. 



• Presented to the Imperial Geographical Society of Russia, December 4, 

 1874 ; read at the monthly meetuig of the Society, December 16, 1874. 



A very rough calculation, founded on the scanty data to be 

 found in General Ivanien's painphlet on Khiva, and made by me 

 some four months ago, gave 30,000 cubic feet per second as the 

 quantity of water diverted from the Amii by the irrigation canals. 

 It is to be remarked, however, th.at the few dimensions civen of 

 tliese c.tnals are merely founded on hearsay evidence, and are 

 not the result of actual careful observation, and they refer, more- 

 over, to the slate of things which existed forty years ago. No 

 correct estimate can be expected to be deduced from such con- 

 fessedly general and incomplete information. It results, then, 

 that the first estimate of 40,000 cubic feet per second, founded 

 on the known necessities of the land and its population, is 

 probably nearer the truth than the second, which I derived 

 from a perusal of General Ivanien's interesting pamphlet. 



It has already been said that the heads of the canals remain 

 open during the flood season of the Amii ; the quantity of water, 

 consequently, entering the canals, depends upon the height of 

 tlie summer floods of the river, and will be greater as the level 

 of the flood is higher, and will be less as that level is lower. But 

 .since a supply of about 40,000 cubic feet per second is a matter 

 of actual necessity to the lives of the population of the Khanate, 

 it is clear that the levels of the canal beds, at their heads, must 

 be so adjusted as to provide for the entry of 40,000 cubic feet 

 per second, even should the level of the Amii flood be an excep- 

 tionally low one. It results, therefore, that in all years, except 

 that of an exceptionally low flood, a much greater quantity of 

 water than what is actually required for irrigation and for con- 

 sumption by the population and by the cattle is diverted from 

 the Amii, and passes by the irrigation canals of Khiva. Ivanieu 

 mentions that the excess of water passing by the canals during 

 high floods is allowed to flow into lakes .and into the Doudon, 

 Kunya Darj'alik, and other old dry beds of the Amii, which 

 thus act as safety-valves to the embankments and works belonging 

 to the irrigated tract. The conclusion which may be drawn 

 from the foregoing is, that in most years there is a very great 

 waste of water arising from the imperfect system of irrigation 

 employed in Khiva. It is needless to enlarge on the magnitude 

 of such an evil in a locality where water is an absolute necessity 

 to prevent the advance of the surrounding desert. With a scien- 

 tific system of irrigation, it is probable that an acreage of land 

 equal to that at present cultivated on the banks of the Amii 

 might be reclaimed from the desert, by precisely the same expen- 

 diture of water which now takes place. 



The following table, which I have ventured to compile from 

 the measurements and observations of the Amii Darya made by 

 the officers of the expedition sent in 1874, under the auspices of 

 the Imperial Russian Geographical Society, will enable some 

 idea to be formed of the waste of water which took place on 

 several dates between the 23rd of June and the loth of Septem- 

 ber of the year in question. The table shows, in cubic feet per 

 second, the total discharge of the river, the portion of that dis- 

 charge diverted by the irrigation canals, and the remainder 

 which passed Nukus. I must, however, remark that the quan- 

 tities shown should be regarded as an approximation only to the 

 truth. 



These figures show that in lieu of 40,000 cubic feet per second, 

 which is the water supply estimated to be sufficient for the wants 

 of the Khanate, the irrigation canals, between the 23rd of June 

 and the loth of September, 1874, diverted, on an average, 

 62,600 cubic feet per second from the Amii Darya, or ten-nine- 

 teenths of the whole volume of the river. 



Information does not yet exist which would allow more than 

 a guess to be made of the volume of the low-water discharge of 

 the Amii, but from what has been already stated, it follows that 

 at Nukus there is a very much less difference between the 



