mann introduces an essay on the Best Time for Determining Altitudes by the Barometer. In continuation of the labors of Ruhlmann, Bauernfeind, Plantamour, and others, he shows that the correct altitude can be deduced from observations on summer afternoons, and that, too, without using the temperature of the upper stations, and even when the stations are at considerable horizontal distances. His method depends on the assumption that the equilibrium of the ascending currents is maintained and expressed by the known laws of thermo-dynamics (as developed quite independently by Thomson, Reye, Hann, and others), and assuming that the ascending currents neither give any heat to surrounding air nor receive any from it or from the sun, or other source. His formulæ thus deduced, and employing for all his physical constants the numbers ordinarily accepted as resulting from laboratory experiments, enable him to compute altitudes up to 7000 feet, with an extreme error of 15 feet when he uses monthly means of observations in July at 1, 2, or 3 P.M.

Lieutenant-Colonel R. S. Williamson, U.S.E., has published a compendium of his paper on the Use of the Barometer on Surveys, which is followed by a comparison of his method with that of Professor J. D. Whitney, as described in his work entitled "Contributions to Barometric Hypsometry." Colonel Williamson claims to have shown conclusively that Whitney's method gives over 40 per cent. more of maximum and mean errors than does his own.

Major Powell states, in reference to the hypsometric work of his survey in Southern Utah in 1877, that it rests on a primary base established at Mount Pleasant, at which barometric observations were made four times daily, and were also made hourly for eight days of each month. All his camps and observing-stations were connected with the base by barometric observations; but it is recommended that a special series of hourly observations be conducted for a few years upon some of the Rocky Mountain peaks for the purpose of correcting the barometric formulæ now in use. topographic details much use has been made for some years past of the orograph-an instrument devised by Professor A. H. Thompson, and which seems to have been lately reinvented in France.

For

Physical Geography and Geology.

The influence of meteorological phenomena, especially rainfall and rivers, in altering the physical geography, is well illustrated by the following extract from Markham's chapter on the "Physical Geography of India:" "The basin of the Ganges has been minutely examined by the officers who have constructed the works of irrigation, and the physical laws which regulate the great Indian river-systems have been discussed by Mr. Ferguson. The latter shows that all rivers oscillate in curves whose extent is directly proportional to the quantity of water flowing through them. Water resists. water far better than earth does, so that a river can attack its banks in detail and carry the bits away; but still water, by producing a state of rest, forces a river to deposit its silt. Mr. Ferguson concludes, with regard to the Ganges, that from 4000 to 5000 years ago the sea, or at least the tide, extended as far as Rajmahal, and that Bengal proper was a vast bay or lagoon." The gradual raising of the delta is indicated by the positions of the capital cities: thus, 3000 B.C., the only practically habitable part was the water-shed between the Sutley and the Jumna. The first cities really in the plains. were Hastanapura, on the Ganges, and Ayodia, on the Gogra, which flourished from 2000 B.C. to 1000 B.C. Then followed in succession Canonj, afterwards Palibothra, or Patna, then Gour, and, finally, A.D. 1604, Dacca.

A magnificent chart of Europe during the two glacial periods is published by Petermann, in the twenty-fourth volume of the Mittheilungen, in continuation of his earlier paper on the same subject.

Abich contributes a paper on the Glaciers and Snow-lines of the Caucasus. The latter vary from 8000 to 10,000 feet, according to locality. Observations on the movement of the glaciers seemed to give negative results.

T. Sterry Hunt communicates to the Academy of Sciences at Paris some remarks on the Geological Relations of the Atmosphere. He says: "I have been led to see in the carbonic acid discharged from volcanoes and from some springs of gaseous waters, only a product of the decomposition of the carbonates which were previously formed at the surface of the globe, at the expense of the carbonic acid of the atmos

phere. I have shown, moreover, that the formation of the carbonaceous and bituminous matters in the strata of the earth, all which seem to me to have an organic origin, have required a weight of carbonic acid which far surpasses that of our atmosphere, and moreover would have given place to a very considerable disengagement of oxygen resulting from the deoxidation of carbonic acid and water. It is necessary

to admit that this carbonic acid had an extra terrestrial origin. I think we ought to consider our atmosphere as a cosmic and universal medium, condensed around certain centres of attraction in proportion to their masses and their temperatures, and occupying the whole of interstellar space in a state of extreme rarefaction. From this it will result that the surplus of carbonic acid will be absorbed in equal proportions in the atmospheres of all the celestial bodies, and that at the same time any excess of oxygen disengaged at the surface of our globe will be equally divided among all the celestial bodies. This theory of a universal exchange seems to me to furnish an explanation of the origin of cosmic dust."

Botany and Zoology.

The influence of atmospheric electricity upon vegetation has been studied by Grandeau, who communicates his results to the Academy of Sciences at Paris, showing that under large trees, under massive shrubbery, and under a coppice covered with verdure, the electric tension of the atmosphere is sensibly zero, while at the same moment, at a few yards' distance from these conducting bodies, we can demonstrate notable quantities of electricity.

Berthelot communicates to the Paris Academy some interesting remarks in reference to the memoir of Grandeau on the Effect of Atmospheric Electricity. He states that he has discovered that the free nitrogen in the air unites with organic matter under the influence of electricity, not only when strong tensions are employed in the experiment, but also with very feeble tensions. He again calls the attention of meteorologists and farmers to the importance of the continued action of atmospheric electricity of feeble tension to the fertilization of the soil.

The Influence of Temperature on Vegetation was treated of by Goppert, in which he explains why it is that great ex

tremes of cold, lasting but a short time, are less injurious than less extreme temperatures lasting for a longer time. Middendorff concluded from his observations in Siberia that the frozen stems and roots could perhaps exist in that condition for many years without injury, with which conclusion Goppert unites his own observation on the revival of vegetation that had been buried for many years under glaciers. He gives an extensive list of plants, and low temperatures which they are able to endure with impunity.

Dr. Sorauer communicates to the Botanische Zeitung for January some observations on the Influence of Moisture on Vegetation. He finds that in dry air branching is greater than in moist air, the length of the leaves is less and the breadth greater, and a moist atmosphere is more favorable to the length of leaf-sheaf, to the growth of the principal stem, and also to the development of the root. In dry air the epidermal cells of the leaves were more numerous and broader, the cells between the stomata shorter, and the stomata themselves shorter and more numerous than in moist air.

Among other papers bearing on the relation between meteorology and botany, we note a paper by Professor Rein on Mountain and Valley Winds, and their Effect upon the Vegetation of Volcanic Mountains, read at Cassel.

C. Eder, in an inaugural dissertation at the Leipsic University, republished by the Vienna Academy of Sciences, investigates the Quantity of Aqueous Vapor Expired by Plants, and concludes that the transpiration is a purely physical process, modified by numerous physical conditions, principally by the relative humidity and the quantity of water the air is able to contain, by the temperature, and by the wind. Light of itself has no influence. There is no periodicity except as determined by these exterior circumstances.

Lauterburg contributes to the Basle Association an excellent paper on the Influence of Forests upon the Springs and Rivers of Switzerland. Culmann, in some appreciative remarks, endorses the desire for a system of telegraphic predictions of approaching river floods, etc., in Switzerland.

The fluctuations in the level of the Great Salt Lake have been especially studied by Mr. G. K. Gilbert, of Powell's Survey, who finds that since 1869 there has been no great change in the water-level, which now averages 10 feet above its level.

in 1847. The total area of the water-surface has increased by about 25 per cent., by which expansion the surface for evaporation was increased. This extension of the lake is shown to be clearly an anomaly in its history, and to explain it Mr. Gilbert states that he has reason to believe that the industries of the settlers have so modified the surface of the land that a larger share of the snow and rain finds its way into the watercourses and the lake. He believes that the tax imposed upon the streams by the work of irrigation is more than repaid by the effects of the draining of marshes and the destruction of herbage and timber.

The influence of wind and climate upon the migrations and spread of the grasshoppers has been very fully considered in the reports of Riley and Whitman, State entomologists for Missouri and Minnesota respectively (see also the report for 1876 of the Commissioner of Statistics for Minnesota). The report for 1877 of the United States Entomological Commission is remarkably full on this point.

Hellmann, in Petermann's Mittheilungen, calls attention to the possibility of predicting the invasions of grasshoppers or locusts, which, leaving the Sahara in the spring with southwest winds, are carried over Algeria and Egypt, and do more damage than the severest storms. A similar duty has been frequently urged by Dr. Packard and others upon our Signal Service; and in this connection it may be well to call attention to a theoretical explanation of the grasshopper migrations which has lately been proposed by Abbe, and which is said to account for most of the phenomena that have been observed. According to this explanation, the grasshopper is an insect at home and comfortable only in a rather dry atmosphere, and possibly a diminished atmospheric pressure; air that is either too dry or too moist is equally liable to make the insect uncomfortable, and in either case he seeks relief in flight, not knowing whither he shall go. Now the very dry winds are the westerly winds, that bear him rapidly eastward to the Missouri and Mississippi valleys. The very moist winds are the south and southeast winds of the Mississippi valley, that bear him or his progeny in the next year back to his original breeding-grounds. It will be curious to show whether this hypothesis holds good for the African as well as it does for the American insect.