544 



NA TURE 



'[April 7, 1 88 1 



colours with different inteasities of light (Pfluger's Archiv, v, 

 24, p. 189). From a large number of measurements it v\as 

 found that, on an average, the red-colour sensation first occurred 

 with a light-quantity equal to 3-55^, v\ hile for blue the lowest 

 amount of light was 353-1^- Thus blue gives a sensation uith an 

 amount of light sixteen times less than that required for red. 

 AVith rise in the degree of brightness, the increase of sensibihty 

 to red proceeds pretly regularly ; but for blue the increase 

 becomes gradually greater (with the weakest degrees of brij;ht 

 ness this increase was = o'22, with the strongest 0'82, witli the 

 mean 0'36). Comparing the two sensibilities together, from 

 the maximum of light strength to the minimum, the sensibility to 

 blue is always found to exceed that to red (maximum thirteen 

 and a half times, minimum sixteen times, mean four times). 



IsoETES LACUSTRIS. — In an interesting paper read before the 

 Academy of Sciences of Paris (January 10, 1881), M. E. Mer 

 calls attention to the peculiar conditions under which dift'erent 

 forms of this fresh-water plant seem to originate in the Lake of 

 Longemer. The basin of this lake was once occupied by a 

 glacier, and now presents several different sorts of bottom. The 

 soil to a depth of two to three metres is composed in part of a 

 gravel formed of rock dSris united by an iron cement, in part 

 of ancient moraines, or where near the surface these will be 

 mixed with the remains of plants and form a pretty tenacious 

 mud. In all these situations Isoetes is to be found, but the 

 plants differ most remarkably both as to their form, their struc- 

 ture, and their mode of reproduction as they are found in tlie 

 different habitats. Taking the leaf-development as a guide, fjur 

 varieties are easily discerned : — (i) /iu?nilis, growing sparsely in 

 the gravel and sterile shallows, the leaves are not only few in 

 number, but always of diminutive dimensions ; sporange generally 

 wanting or represented by a small cellular mass which rarely 

 ever forms a propagule, and then these with puny leaves ; (2) 

 stricta, found on the borders of the lake or in the old alluvial, 

 therefore in less sterile quarters than the preceding ; leaves mrire 

 numerous, stout, but still of small size ; (3) intermedia, grow ing 

 on ground formed of a mixture of mud and clay, either on 

 the borders of the lake or at a dejith of from one to two metres, 

 leaves quite intermediate in character between the previous variety 

 and the next ; (4) clatior, growing on the clayey depths, with 

 long leaves. The first form is always found isolated, and as to 

 its asexual reproduction there is nothing more to be said ; but 

 the o;her three, according as they are subject to more or less 

 heat, present each three varieties characterised by the mode of 

 reproduction, i. Sporifera, isolated individuals, mostly furnished 

 with well-developed sporangia, stem large, roots numerous, leaves 

 large. 2. Gemi)iifcra, few fertile sporangia, but most of the 

 leaves are furnished with propagula, and these well furnished 

 with leaves, generally dextral, stem fairly developed. 3. SteriHs, 

 individuals growing in compact masses, stems and roots slender, 

 leaves not numerous, long and narrow, fertile sporangia very 

 rare, and more often imdeveloped masses of cells or abortive 

 propagula. It would seem as if these facts had a practical 

 interest to the collector, who may find in them a guide as to 

 where to look for fertile specimens. 



GEOGRAPHICAL NOTES 

 On Friday, April i, the French Geographical Society held a 

 meeting in the large hall of the Sorbonne for the reception of 

 Dr. Lenz on his return from Timbuctoo. M. Milne- Edwards 

 was in the chair. Dr. Lenr, as our readers know, has been 

 very successful, although his conclusions are adverse to the con- 

 struction of a railway from the Niger to Algeria throughout 

 the Sahara. On the following morning the Society received 

 a telegi-am stating that Col. Flatters had teen murdered by 

 Touaregs at some distance from the Lebhkha Amagdor. In the 

 evening the sad news was confirmed by an official message, stating 

 that four starving Arabs from the mission had arrived at Ouargln, 

 and that the Khobfa had left ^\ ith four hundred mehari and 

 camel horsemen to rescue the survivors, who were besieged south 

 of Messaguer in the Touat region proper. Happily the neus of 

 the disaster to Col. Flatters' expedition has not yet been further 

 confirmed, and authorities in Paris are inclined to believe that it 

 has been much exaggerated, and that the story of the four natives 

 has many elements of suspicion about it. 



Dr. Lenz, in bis lecture at Paris, gave some interesting details 

 on the present condition of Timbuctoo. Its houses are built of 

 brick, and the population is now only 20,000. It has greatly 



decayed, and the inhabited part of the town is surrounded by 

 great spaces covered with ruins. There are numerous schools 

 and rich libraries. Dr. Lenz had a cordial reception, and every 

 night during his twenty days' stay he was present at religious 

 conferences which the learned men of the city held with his 

 interpreter ; the commentaries on the Koran formed the only 

 subject of conversation. Tmibuctoo is united with the Niger, 

 six miles off, by a series of lakes, formerly canals. Dr. Lenz 

 has also made some interesting observations on the Sahara, 

 tending to confirm the conclusions of Rholfs 'and other recent 

 scientific travellers as to the variety which is to be met with in 

 the great desert. It is really a plateau about 300 metres in alti- 

 tude, no part of it being below the level of the sea. Granite 

 hills, sandy 1 lains, shallow lakes, fertde oases, alternate over 

 nearly the whole surface, while beasts of prey are rarely to be 

 met with. Dr. Lenz will contribute a full account of his journey 

 to the Berlin Africa Society, in whose journal many of his letters 

 have already appeared. 



It is with sincere regret that we record the death of Lieut. 

 Karl Weyprecht, at the age of forty-three, on March 29, of 

 consumption. Lieut. Weyprecht will be known to our readers 

 as the discoverer, with Lieut. Payr of Franz-Josef Land, in the 

 Austro- Hungarian Expedition of 1872-4. His observations on 

 the aurora borealis were of especial value, and he has published 

 several papers on the vubject. He was also the originator of 

 the scheme for establishing a series of international observations 

 around the Pole, which is likely to be realised next year. 



The Rev. G. Brown, the well-known representative of the 

 church militant in the South Pacific, contributes to the new 

 number of the Geographical Society's Proceedings a paper de- 

 scriptive of a recent journey which he has made along the coasts 

 of New Ireland and the adjacent islands, the latter including 

 Sandwich Island, Portland Islands, and New Hanover. Dr. 

 Benjamin Brad^havv, who has spent some years in collecting 

 natural history specimens in the Upper Zamliesi region, also 

 contributes a brief paper on the Chobe River, together with a 

 sketch-map of a portion of its course, adding materially to our 

 knowledge of the geography of this regiun. Mr. Crocker's 

 paper on Sarawak and Northern Borneo, lately read before the 

 Society, is also given, and is illustrated with a good map. The 

 geographical notes are full of interesting matter, one giving an 

 accrunt, by Mr. Sibiriakoff him-elf, of the voyage of the Oscar 

 Dickson to the Yenisei Gulf in 1880. Another furnishes con- 

 clu^ve proof of the usefulness of the course of scientific instruction 

 provided by the Council for intending travellers in foreign 

 countries. From the la^t note we learn that Mr. C. K. Mark- 

 ham, the indefatigable secretary, is preparing fur the forthcoming 

 volume of the Journal a sketch of the Society's work in the 

 past fifty years. 



In the current number of Les Missions Catholiques, Pere 

 Richard, a missionary in Algeria, commences an acC'iunt of his 

 journey, in company with Pere Kerniabcn, among the Tuareg- 

 Azguer tribes of the Sahara. The object of their journey was 

 to study this almost unknown reL'ion, and to cultivate friendly 

 relations with the chiefs and people generally with a view to the 

 formal ion of a mi^>ionai-y station. The mote interest attaches 

 to Pere Richard's narrative, a> it deals with the very region 

 which Col. Flatters has been now exploring with the object of 

 settling the best practicable ruute for the projected Trans-.Sahara 

 railway. An entirely new map of this part of Africa, based on 

 Pere Richard's notes, accompanies the number. 



A lately-issued batch of Reports from H.M. ' onsuls (Part 

 vi. of last year) contains useful geographical information respect- 

 ing portions of South America, that relating to Chili and Peru 

 being specially interesting at the present moment. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



CamisRIDGE. — On the 31st inst.the honorary degree of LL.D. 

 was conferred on Prof. Helmholtz of Berlin at a special congre- 

 gation. 



Prof. Humphrey will take his usual May classes for the second 

 M.B. and Natural Sciences Tripos next term, and the demon- 

 strator will give demonstrations cf the organs. 



Prof. Babington will lecture on botany four times a week next 

 term, beginning April 26. Mr. Hillhouse will give lectures on 



