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SCIENCE. 



[Vol. XVI. No. 394 



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Vol. XVI. NEW YORK, August 33, 1890. 



CONTENTS: 



The Time-Relations op Mental 



Phenomena. Joseph Jastrow 99 

 Legislation on Pood Adultera- 

 tion. Edgar Richards 101 



Notes and Nkws 104 



Oriqin and Character of the 



Sahara 1 06 



Health Matters. 



Sea Air for Phthisis 107 



Death from Tight Lacing 107 



Restriction and Prevention of 

 Diphtheria 107 



Disappearance of Small-Pox in 



Germany 107 



Treatment of Snake-Bites 107 



Surgeon Parke on Vaccination . . 108 

 Letters to the Editor. 

 Wind-Systems, il. A. Veeder. . . 108 

 On the Lack of the Distance- 

 Sense in Prairie Dogs 



Burt G. Wilder, M.D. 108 

 Ballooning of Spiders 



F. Macloskie 108 

 Among the Pfblishers 108 



ORIGIN AND CHARACTER OF THE SAHARA. 



At tbe annual meeting of the Scottish Meteorological Society on 

 July 13, Dr. John Murray read an interesting paper, a summary 

 of which is given in the August Proceedings of the Royal Geo- 

 graphical Society. In his paper, Dr. JIurray treated of the me- 

 teorological conditions of desert regions, with special reference to 

 the Sahara, the northern border of which he had recently visited. 

 He pointed out that the arid regions of the world are distributed 

 in two bands, north and south of the equator. They are all in- 

 land drainage areas, or areas where the streams have no connec- 

 tion with the sea. They are also regions where evapoi-ation is in 

 excess of precipitation, for if the latter were in excess the water 

 would rise till it could flow into the sea, as in the case of the great 

 lake district of North America, and the area would no longer be 

 one of inland drainage. The largest of the deserts, the Sahara, is 

 about three and a half million square miles in area, and the area 

 of all the deserts of the world together is about 11,500,000 square 

 miles That is to say, over one-fifth of the land of the world has 

 no outlet for drainage to the sea, and in all that area evaporation 

 is greater than precipitation. These areas correspond very closely 

 with the regions of the world where the rainfall is less than ten 

 inches annually. In no place in the world can there be got such 

 enormous changes of temperature as in the deserts. In the Sa- 

 liara the temperature sometimes falls from 100° during the day 

 to the freezing point during the night. This arises from the great 

 dryness of the atmosphere, and from the radiation that takes 



place from tbe burning soil after the sun has set. These inland 

 drainage areas correspond very much in their barometric phe- 

 nomena. In all desert regions during summer all winds blow in 

 to them. In winter the reverse takes place, tbe winds flow out 

 of them ; and that holds good both for the northern and the 

 southern hemispheres. This leads to the low rainfall, for the 

 great majority of these regions are more or less bounded by high 

 hills. The winds come into the deserts over these hills, and the 

 vapor is precipitated from the atmosphere by the hills, with the 

 result that when the. winds reach the interior regions there is 

 nothing left to be deposited. If there are not hills all round any 

 desert area, then, as i)i the case of Northern Asia, the winds pass 

 from a colder to a warmer climate, and as they get to warmer re- 

 gions they are able to contain more vapor, and none is precipi- 

 tated. 



Dr. Murray then proceeded to give an account of his own views 

 and impressions as to the Sahara. During the " Challenger" ex- 

 pedition he and his companions had found in the bed of the At- 

 lantic for a long distance west of the African coast opposite the 

 Sahara, and in the bed of the Indian Ocean to the south of Aus- 

 tralia, small grains of red quartz sand; and they bad found 

 scarcely a trace of such in the sea-bed in any other ijart of the 

 world. He suspected this quartz sand had been blown out from 

 the Sahara in the one case, and from the Australian desert in the 

 other. On his journey southward through Algeria, he found the 

 country as far as Tougourt converted into a garden by means of 

 artesian wells. At Tougourt the real sandy part of the desert be- 

 gan, and he made excursions into it, with that town as his head- 

 quarters. He exhibited to the meeting a specimen of the sand, 

 of a light yellowish-brown color, and exceedingly fine in the 

 grains. There were, he said, a good many clay jjarticles in it, 

 and the quartz particles, which were also numerous, were identi- 

 cal with those they had got in the bottom of the Atlantic. There 

 was no doubt that the winds from the desert carried the sand a 

 long way out to sea. 



He had also examined the region geologically, and found that 

 the formation of the rocks was entirely that of fresh water, and 

 of quaternary date. The great majority of geographers and 

 geologists have expressed the belief that the whole of the Sahara 

 is an old sea-bed, but in his opinion, it has never as a whole been 

 covei'ed by the sea since Cretaceous or Devonian times; and no 

 part of it has been covered by the ocean since Tertiary times. The 

 whole question about the discovery of shells seems to rest upon 

 one common species being found very rarely in one region of the 

 desert. Owing to recent researches, the opinion as to the Sahara 

 being an old sea bottom is very likely to disappear from our text- 

 books. He considers that the features of the region have been 

 produced by atmospheric conditions. The sand is the product of 

 the disintegration of the rocks in situ. The existing rock is not 

 far below the surface, and by digging down to it, the hard sandy 

 particles are found embedded in the stone. The sun shone on the 

 rocks, and they e-xi^anded. The sudden cooling at night broke 

 them up, the wind carried away the smaller particles, and so con- 

 tinually the rocks are being disintegrated by means of changes 

 other than water, although water perhaps in times past played a 

 greater role there than it does now. There is a range of hills in the 

 desert, seven thousand feet high, and for three months in the 

 year their summits are covered with snow. Descending the hills 

 are old river-courses, some of great length. Much of the region, 

 he considers, has once been a large fresh-water lake. Speaking 

 of the commercial aspect of the Sahara, he said it was difficult to 

 go there without becoming enthusiastic about it. There seems to 

 be no limit to tbe amount of water that is to be got by sinking 

 artesian wells. The cultivation of palms is extending to an 

 enormous extent, and the French expect to carry on their railway 

 to Tougourt, at present nearly a week's journey from Algeria, in 

 the next few years. 



BrLLETiN No. 7, July, 1890, just received from the Virginia 

 Agricultural Experiment Station, treats of tests with varieties of 

 strawberries made the present season, giving full discussion, with 

 critical descriptive notes of forty-nine varieties; also full tabular 

 statements showing yields, earliness, quality, etc. 



