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THE POPULAR SCIENCE MONTHLY. 



as a great step in advance in the method of 

 the variation of the elements and in theoret- 

 ical dynamics generally. The two sets of 

 planetary tables are works of immense labor, 

 embodying results only attainable by the 

 exercise of such labor imder the guidance 

 of profound mathematical skill — and which 

 are needed in the present state of astronomy. 

 I trust that, imperfectly as my task is ac- 

 complished, we have done well in the award 

 of our medal" 



Nature's Distribution of Trees.— In a note 

 presented to the Philadelphia Academy of 

 Sciences, Mr. Thomas Meehan held it to be 

 an error to suppose that trees are by nature 

 placed in conditions best suited to their 

 growth. Almost all of our swamp-trees grow 

 much better when they are transferred to 

 drier places, provided the land is of fair 

 quality. He referred, among others, to sweet 

 bay, red maple, weeping-willow, and other 

 trees, as within his own repeated observa- 

 tions growing better out of swamps than in 

 them. The reason why they originate in 

 swamps is that their seeds can germinate 

 only in damp places, and, of course, in the 

 state of nature, the tree remains where the 

 seed has germinated. Plants, as a general 

 rule, even those known as water-plants, pre- 

 fer to grow out of water, except those which 

 grew almost entirely beneath the surface. 

 The TazodiiLm distichum^ in the Southern 

 swamps, sends up "knees" from various 

 points, often as large as old-fashioned bee- 

 hives, and several feet above the surface. 

 Not only is the cypress as large when grow- 

 ing in good, rather dry ground, as when 

 growing in swamps, but the tendency to 

 throw up these knees is in a measure lost. 

 With the general facts before us, of the an- 

 tipathy of swamp-plants to submersion, Mr. 

 Meehan thinks it safe to conclude that ■ 

 these root-excrescences were the result of 

 an effort of the plant to counteract the law 

 which held it, so to speak, in the place of its 

 birth. 



Determination of Oxygen dissolved in 

 Water. — At the weekly meeting of the Ly- 

 ceum of Natural History on Monday, Feb- 

 ruary 16th, as we learn from the Engineer- 

 ing and Mining Journal^ Prof. Wurtz read 

 a paper on subaerial oxidation. The author 



is well known to have been for some time en- 

 gaged in the study of the problems connected 

 with the water-supply of cities. Among 

 these problems,the question of what becomes 

 of the nitrogenous compounds contained in 

 sewage when poured into a running stream, 

 is one of the most important. Oxidation 

 goes on by the action of oxygen dissolved 

 in the water, and Prof. Wurtz has long been 

 studying the means of ascertaining the pres- 

 ence of oxygen in a given water, and of 

 measuring its quantity. To do this he uses 

 a color-test, employing for that purpose 

 pyrogallene, which turns brown under the 

 action of even infinitesimal quantities of 

 oxygen. A sample of water is first made 

 alkaline, and then a drop or two of a con- 

 centrated solution of pyrogallene in alcohol 

 is added. If oxygen is present, the result is 

 a brown tint ; but, if an aqueous solution of 

 pyrogallene is used, a beautiful pink is some- 

 times produced. With liquids containing 

 infinitesimal quantities of oxygen, the aque- 

 ous solution of the reagent gives a pink 

 color which gradually passes to purple and 

 finally to brown. The depth of the color, 

 therefore, varies with the amount of oxygen, 

 and permits the estimation of the quantity 

 present by the use of graduated standards. 



English Fish in Indian Waters. — In De- 

 cember, 1867, Mr. Mclvor, Superintendent 

 of the Chinchona Plantations, on the Nil- 

 ghiri Hills, in Southern India, took out 

 carp, tench, trout, and other fish, with 

 which he has now stocked the rivers, 

 streams, and lakes, of the Nilghiris. The 

 trout have not succeeded well, but the 

 growth and increase of the tench have been 

 marvelous. The first English fish were put 

 in the lake at Utakamund, in August, 1869. 

 In 1871 and 1872 the streams flowing into 

 the lake were well stocked with fish, and 

 for the last few months they have been 

 caught in large numbers by the natives, and 

 sold in the markets. The tench greatly 

 predominate. One interesting fact is that 

 many European fish have been caught be- 

 low the great Kalhutty water-fall, showing 

 that they have survived after being carried 

 down the highest fall from the Nilghiris, in 

 the descent of the Utakamund Lake and 

 River to the plains. It may, therefore, be 

 expected that the rivers from the foot of the 



