'234 



NATURE 



\Jan. 17, iS7« 



of the Museum of Natural History at Milan, has been decorated 

 by the Emperor of Russia with the order of St. Ann for his 

 efficient co-operation in the foundation of the institute for 

 " Bachicoltura " at Moscow and Tashkend. 



The scientific expedition to Lake Lob-Nor, sent out by the 

 St. Petersburg Geographical. Society, under command of Col. 

 Prjewalski, and to which we have already referred, has yielded 

 most interesting results in every direction and is of particular 

 importance with regard to the exploration of Kashgar. The 

 new details obtained in reference to Lake Lob-Nor are re- 

 markable. The expedition continued its way from Korla, 

 following the course of the Tarim River down to its confluence 

 with the Rokala Darja. On their way to the Lob-Nor the 

 travellers passed the ruins of three cities. Lake Lob-Nor is of 

 a marshy nature ; its length is some 100 kilometres, by only 20 

 kilometres breadth. Col. Prjewalski explored the western 

 and southern shores, and through the current of the Tarim 

 River reached the middle of the lake. There the shallowness 

 of the water and impenetrable vegetation prevented further pro- 

 gress ; almost the whole surface of the lake is thickly covered 

 with reedy vegetation. The inhabitants of the Kara Kurchintz 

 district, on the shores of Lake Lob-Nor, are on the lowest step 

 of civilisation. They live along the shores as well as on islands 

 in the lake, in miserable huts constructed of reeds and branches 

 twisted together. The whole of their possessions are their 

 clothes, which barely cover their nakedness aiad are made of the 

 fibres of a kind of lake weed, their nets, and their canoes, which 

 are hollow trunks of trees. Metal, objects, such as knives, 

 hatchet?, &c., are extremely rare among them. Col. Prje- 

 walski, besides his ethnographical results, has collected rich 

 materials for ornithological investigations. He reports that it is 

 impossible to conceive the enormous number of migratory birds 

 which, on their journey from southern countries to the north, or 

 vice versd, select Lake Lob-Nor as a halting place. At present 

 the Russian traveller has wended his way southward and is 

 engaged in the exploration of Tibet. 



In an interesting paper, published by M, Ph. Plantamour in 

 the December number of the Archives cJes Sciences Physiques et 

 Naturelles (Geneva), regarding the earthquake experienced in the 

 immediate neighbourhood of the Lake of Geneva on October 8 

 last, the author proves most conclusively that the phenomena 

 known under the name of " Seiches," and consisting in occa- 

 sional and sudden alterations in the level of the lake, have 

 nothing whatever to do with upheavals or depressions in the bed 

 of the lake. During the earthquake referred to, not the least 

 movement of the surface was perceptible, and had an alteration 

 of only one millimetre taken place in the level, the instruments 

 employed by MM. Plantamour and Forel, which continually 

 register these alterations,, would have most certainly shown them. 

 The explanation of these "Seiches," therefore, is still a matter 

 of considerable uncertainty, and it even remains to be seen 

 whether barometrical pressure has any influence upon them 

 or not. 



Two enterprising men in Paris, a merchant and a doctor of 

 medicine, whose names v/iil be surely blessed by future genera- 

 tions, have made the valuable discovery that the different ele- 

 ments contained in sea-water are infallible preservatives against 

 all possible diseases, and at the same time are never-failing 

 remedies against existing illnesses. These two philanthropists 

 have therefore not only issued a seductive prospectus and widely 

 circulated it in France and abroad, but have also prepared a 

 large quantity of hygienic products, such as bread, biscuits, dry 

 cakes of all descriptions, liqueurs, &c., which are all prepared 

 with sea-water, and are endowed with the most marvellous 

 healing properties. In the prospectus it is stated distinctly that 

 the use of these preparations renders all other medicines or 

 medical treatment unnecessary. There is only one little point 



which requires explanation. The " inventors " state that their 

 preparations are made with distilled sea-water ; we would ask 

 them what becomes of the mineral and organic matter contained 

 in sea- water during this distillation ? But nmitdus vult decipi ! 



The additions to the Zoological Society's Gardens during the 

 past week include a White-handed Gibbon {Hylobales lar) from 

 the Malay Peninsula, a Brown Monkey {Macacus arctciJes) from 

 Burmah, presented by Mr. W. H. Newman ; two Black 

 Francolins {Fraticolinus vulgaris) from India, a Chukar V&x- 

 ir'iAge {Caccabis chukar) from North- West India, presented by 

 Major Newton Paul! ; four Common Marmosets {Hapale jacchus) 

 from Brazil, deposited ; two Rough Termpins (C/cmmys punciu- 

 /aria), a Scorpion Mud Tortoise [Ctnosternon scorpoides) from 

 Trinidad, purchased. 



CERTAIN MOVEMENTS OF RADIOMETERS^ 



'X'HIS morning (Dec. 20) I received from Mr. Crookes an account 

 -^ of the behaviour of a kind of radiometer which he was so good 

 as to construct at my suggestion. The consideration of an experi- 

 ment mentioned in a paper of his presented to the Royal Society, 

 which will shortly be read, and which he has kindly permitted 

 me to refer to, suggested to me the desirability of investigating 

 the elTect of mere roughness of surface, all other circumstances 

 being alike, and the disc of the radiometer being metallic, so 

 that the two faces may be regarded a.= practically at the same 

 temperature. Mr, Crookes's experiment, above referred to, led 

 me to suspect that mere roughness might increase the efiiciency of a 

 surface, and I suggested to him some experiments with heated glass 

 shades, or with a hot poker presented to the radiometer, the bulb 

 being covered with a cool tumbler to defend it from being heated 

 by the rays easily absorbed by glass. The result in every case 

 answered my expectation ; and it may be stated shortly that the 

 law of the motion is that when the fly is hotter than the bulb 

 the rough surface is repelled, or, say, the motion is positive ; 

 wllen cooler, negative. 



I subjoin Mr. Crookes's memorandum of the results of experi- 

 ment : — 



" Ahtminiutn Radiometer (1326), one side of the vanes biin^ ruled 

 closely with a sharp knife. 



" I. Exposed to standard candle three inches off. Continuous 

 positive rotation (ruled side repelled) at rate of 3^ revolutions a 

 minute. 



" 2. Exposed to non-luminous flame of a Bunsen burner three 

 inches off. Continuous /cj/Z/z/t? rotation at the rate of 7 J turns a 

 minute. 



"3. Tiie Bunsen burner removed. The positive rotation 

 gradually dimmished till it stopped. No negative rotation. 



"4. The bulb heated with Bunsen burntr. Good naiative 

 rotation ; then stopped, and roXdiieA positively till quite old. 



" 5. Bulb covered with a cold glass shade, and a lage red-hot 

 ring applied round equatorially. Positive rotation, but not very 

 strong. 



"6. On removing the shade and ring the positive movement 

 soon comes to rest. 



"7. Covered with a hot glass shade, negative rotation, with 

 positive rotation on cooling (ttie same as 4). 



*' 8. Plunged into hot water. Negative rotation. 



"9. Removed from the hot water, and immediately plunged 

 into cold. Positive xo\.z.iion." 



Results nearly identical were obtained with another radiometer 

 described as "silver radiometer (1327), one side coated with 

 finely divided silver, electro-deposited." 



We must accordingly recognise three distinct conditions under 

 which motion may be obtained in a radiometer, namely, (i) 

 difference of temperature of the two faces, as in a pith radio- 

 meter, coated on one face with lampblack ; (2) more favourable 

 presentation of one face than the other, as in a radiometer with 

 curved disks ; (3) roughness of surface on one face (if this be 

 really different from 2). These three conditions may be variously 

 combined so as to assist or oppose each other, as the case may 

 be, in producing motion. 



' Paper read at the Royal Society, December so, by Prof. G. C. Stokes, 

 Sec.R.S. Ccntinued from p. 175. 



