174 



NATURE 



[_Dcc. 23, 1880 



Nabchou, buying food from the Tangoutes, who consider 

 themselves as under the rule of the governor of Sining. 

 Twently days later the answer arrived ; a messenger from 

 the Dalai Lama, accompanied by seven officers, entreated 

 M. Prshevalsky to return, saying that the whole popula: 

 tion of Lassa was very excited against the strangers, as 

 it was declared among the people that the expedition 

 intended to steal the Ualai-Lama himself and extirpate 

 the Buddhist religion. A conflict with the inhabitants of 

 Lassa being most probable, M. Prshevalsky was com- 

 pelled to return. All December and January were spent 

 on the road to Tsaidam, the distance from Nabchou to 

 Tsaidam being 560 miles. Progress on this high plateau 

 (14,000 to 16,000 feet) was very difficult ; out of thirty- 

 four camels twenty died, and the collections were con- 

 veyed on horseback ; the men mostly went on foot. We 

 need scarcely say that the scientific collections and obser- 

 vations are of a great value. 



On March 20 M. Prshevalsky reached the Chinese 

 town of Sining, close to Lake Koko-nor. After having 

 received permission from the governor of the province to 

 go to the Hoang-ho, however, without crossing it, M. 

 Prshevalsky sent his collections to Alashan, and went 

 east to the banks of the Yellow River, which are fifty-six 

 miles distant from the town of Donkyr. He reached 

 them at the Gomi settlement. The river, 450 feet wide, 

 and Sooo feet above tlie sea-level, is rapid (5 feet in a 

 second). Its valley cuts deeply into a great deposit of 

 clay, gravel, and boulders, the abrupt walls of which, along 

 the banks of the main river, being 1600 feet high, and no 

 less than loco feet along the banks of numberless tribu- 

 taries. The journey across these gigantic ravines with 

 abrupt walls (quite like those of the loess in the lower 

 parts of the Hoang-ho) was most difficult. After a 

 journey of 130 miles up the Hoang-ho, AL Prshevalsky 

 reached a lofty mountain-range, which is cut through by 

 the river, and probably is a continuation of the Burkhan- 

 buda range. Further advance along the banks was 

 impossible, and ]\I. Prshevalsky not having a guide for 

 crossing the range was compelled to return and soon 

 reached the town Gui-doni, situated on the left bank of 

 the Hoang-ho, forty miles below Gomi. The natural 

 history collections from the Upper Hoang-ho are very 

 rich : 260 species of plants, many fishes, and 500 birds. 

 The astronomical and barometrical observations are 

 numerous. M. Prshevalsky did not reach the sources of 

 the Yellow River, and he supposes that they cannot be 

 reached otherwise than along the Tibetan plateau ; he 

 doubts however that the Upper Hoang-ho makes so great 

 a bend as it is usually shown on our maps. 



The last letter from AL Prshevalsky is dated Gui-ta-din, 

 on the L'pper Hoang-ho. As is known, he returned zia 

 Alashan, and is expected at St. Petersburg by the end of 

 January. 



MICHEL CHASLES 



THE news of the death of Michel Chasles, perhaps the 

 oldest and best-known mathematician in Europe, 

 will be everywhere learned with deep regret. For the fifty- 

 five years over which his writings extend he has devoted 

 himself with persistent industry to the history of geometry 

 and to the perfection of those geometrical methods with 

 which his name will be always associated. The "Apercu 

 historique sur FC rigine et le Dc'veloppement des Mc- 

 thodes en Gcomctrie," which in fact forms an elaborate 

 history of the subject from the time of Thales and Pytha- 

 goras to the beginning of the present century, is the best 

 known of his works ; it was first published in 1S37, and a 

 second edition appeared only a few years ago. His 

 restoration of the Porisms of Euclid was published in 

 1S60. The last great work of Chasles related to the 

 investigation of the number of conies satisfying any five 

 conditions : the special method which he invented for 



these researches, termed by him geometrical substitution, 

 involved the consideration of the characteristics of 

 systems of conies, i.e. of the numbers of conies satisfying 

 four common conditions and (i) passing through an 

 assumed point ; (2) touching an assumed line. 



In 1865 Chasles received the Copley medal of the 

 Royal Society ; this medal has, since its foundation in 

 1731, been given only five times for discoveries in pure 

 mathematics, viz., in 17S4 to Waring, in 18 14 to Ivory, in, 

 1 84 1 to Sturm, in 1S65 to Chasles, and in the present 

 year to Sylvester. 



In 1846 Chasles was appointed to fill the new Chair of 

 Modern Geometry, founded by the Faculty of Sciences 

 at Paris ; and as a professor he exerted personal influence 

 over the younger geometers of that time, which has since 

 been apparent in their writings, although the effect of the 

 geometrical methods to which he devoted his life is 

 chiefly visible in the works of the Italian and German 

 mathematicians. He was the inventor of the term "an- 

 harmonic ratio," but not of course of the ratio itself, 

 which was known to the ancients. Chasles's memoirs on- 

 the attraction of ellipsoids are well known to English 

 mathematicians and physicists ; and a translation of his 

 memoirs on Cones of the Second Order, and Spherical 

 Conies, was published in Dublin in 1841 by Dr. Graves, 

 now Bishop of Limerick. 



Most of our readers will remember how in 1866 Chasles 

 was deceived by M. Vrain Lucas by what were called the 

 Pascal forgeries, and they will also remember how honour- 

 ably he extricated himself from the matter, and did all in 

 his power to repair the mischief done. The forger was 

 convicted and sentenced to two years' imprisonment ; 

 and not a shadow of suspicion was ever thrown upon 

 the honour or good faith of Chasles. 



Scientific visitors to Paris will miss a well-known face 

 at the .Academy and a kind and hospitable friend. Till 

 quite recently Chasles seemed as active as ever, both, 

 mentally and physically, and it was only last September 

 that he issued a new edition of his " Gifom^trie superieure." 

 He was a Foreign Member of the Royal Society and o£ 

 the Cambridge Philosophical Society. 



THOMAS RYMER JOAES, F.R.S. 



THE late Professor of Comparative Anatomy at 

 King's College, London, whose death is announced,, 

 was born about the year 1820. He studied for the 

 medical profession at Guy's Hospital, and took the 

 diploma of the Royal College of Surgeons, London, in 

 1833. A chronic deafness unfitting him for the ac- 

 tive pursuit of his profession, he devoted hi; attention 

 exclusively to comparative anatomy. Some of his earliest 

 papers were on the dissections of a tiger {Proc. Zool. 

 Soc. 1834) and of an agouti {Proc. Zool. Soc. 1834). He 

 was the first Professor of Comparative -Anatomy at 

 King's College, and was FuUerian Professor of Physio- 

 logy to the Royal Institution in 1840. He was Assistant- 

 Secretary to the Section of Zoology and Botany during 

 the eighth meeting of the British Association held at 

 Ne'.vcastlc-upon-Tyne in i83S,the president of the section 

 being Sir W. Jardinc, the secretaries J. Edward Gray, 

 Rich°ard 0«en, and John Richardson. This meeting was 

 marked by the presence of Christian Gottfried Ehren- 

 bero-, who laid before the section a copy of his famous 

 work, "Ueber Infusionsthierchen," making at the same 

 time a short statement as to his views of the alimentary 

 canal of the polygastric infusoria. These views were, in 

 the discussion which followed, criticised by Rymer Jones, 

 who stood almost alone among the British naturalists m 

 opposing them. In 1S38 the first part of his " General 

 Outline of the Animal Kingdom" was published by 

 Mr. Van \^oorst, happily still among us. It was 

 completed in ten or twelve parts, and was illustrated 



