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THE POPULAR SCIENCE MONTHLY. 



est-continucd convulsions, M. Delaunay sug- 

 gests, take place when two large planets 

 pass by the cosmic groups at the same time. 

 Of this character were the earthquakes of 

 1755, 1Y83, 1829, and 1841. Accepting 

 these principles as the laws regulating the 

 occurrence of earthquakes, and admitting 

 that certain of the cosmic groups may have 

 a slow oscillatory motion around a mean 

 position, it is not difficult to predict when 

 earthquakes may be looked for. M. Delau- 

 nay ventures to predict the dates at which 

 the earthquakes to occur between this time 

 and 1920 will, according to his theory, be 

 due. The most important earthquake peri- 

 ods will probably occur in the years and 

 groups of years 1886, 1890-'91, 1898, 1900- 

 '01, 1912-'13, 1914, 1919-'20, The next 

 seismic tempest may be expected to follow 

 the passage of Jupiter through the zone of 

 the August meteors in 1883. 



Do Stenclies cause Disease ? The peo- 

 ple of Paris were frequently annoyed dur- 

 ing the last summer by the presence of mc- 

 phitic odors in the atmosphere. A commis- 

 sion, appointed to discover the origin of the 

 smells, traced them to certain establish- 

 ments in the neighborhood where refuse 

 matter is manufactured into fertilizers. M. 

 Bouchardat, of the medical faculty of Paris, 

 has examined the question of the effect of 

 these emanations upon health, and has con- 

 cluded that they are innocent. He does 

 not believe that they convey with them the 

 germs of disease, and finds that the gases 

 of which they are composed do not load the 

 air enough to produce a perceptible poison- 

 ing. Moreover, no injury to health has 

 been traced to them. Assuming that con- 

 tagious diseases should manifest themselves 

 within eight or ten days after the germs 

 have been planted, the weekly health bul- 

 letins of the year have been examined to 

 learn if any increase of mortality followed 

 the prevalence of the unpleasant odors. No 

 such increase has been detected, but the 

 mortality seems rather to have fallen off. 



Mr. Thomson's Journey in Eastern 

 Africa. Mr. Keith Johnston was dispatched 

 by the London Geographical Society, in 

 18*78, with an exploring expedition to East 

 Africa, charged with examining the coun- 



try in the neighborhood of Lakes Tangan- 

 yika and Nyassa. Mr. Johnston died at Bc- 

 hobeho, just at the borders of the objec- 

 tive region of the expedition, on the 23d of 

 June, 1879, and the whole responsibility of 

 the undertaking fell upon Mr. Joseph Thom- 

 son, his geologist and general assistant, a 

 young man twenty-two years of age, to 

 whom this was almost the first serious ex- 

 perience in life. Mr. Thomson gave a most 

 interesting account of the expedition, which 

 was attended by unexampled success, at a 

 meeting of the Society on the 8th of Novem- 

 ber last. His story is enlivened with ac- 

 counts of different tribes of the most diver- 

 sified characters and degrees of civilization, 

 living by the side of one another. Leaving 

 Behobeho on the 2d of July, the expedition 

 went toward the west, into the country of 

 the Wakhutu, passing through the valley 

 of the Mgeta, where perennial showers pre- 

 cipitated from the high mountain-range on 

 the right, which forms the ridge of the great 

 central plateau of the continent, stimulate 

 a tropical vegetation to grow and rot in 

 marshy tracts. Under the influence of such 

 an enervating and malarious climate, the 

 1 Wakhutu are one of the most miserable 

 and apathetic races to be found in Africa, 

 and presented a disgusting sight to the 

 traveler as they gathered around him in 

 crowds, " sitting with their miserable, witJi- 

 ered bodies doubled up, and idiotic, lack-lus- 

 ter gaze." Their neighbors, the Mahenge, 

 a hitherto unheard-of tribe, living between 

 the Ruaha and Uranga Rivers, were brought 

 several years ago in contact with a migra- 

 tion of Zooloos, and have adopted the arms, 

 dress, and manners of those people, although 

 in other respects having no affinity with 

 them. To the "Wakhutu the Mahenge are 

 a warlike and dreaded tribe ; to the English 

 traveler, "they were a set, of most arrant 

 cowards, a mean, sneaking, lying race, un- 

 worthy of the name of men." Ten days 

 were occupied in crossing the mountain- 

 ranges that bound the central plateau a 

 charming journey, with diversified scenery 

 and luxuriant vegetation after which the 

 party entered upon a bleak, moorland coun- 

 try four or five thousand feet high, unre- 

 lieved by hill or dale or forest-tree. The 

 scanty population of this barren district of 

 Uhehe are settled in villages at very wide 



