1853] 



RAIN, A SOURCE OF THE NITROGEN IN VEGETATION. 



9 



on the 11th of February at 5-40 a. m., barometer 29-067, ther- 

 mometer 38-5, wind E. by N., velocity 6-00 miles per hour; the 

 wave came from the W. N. W. The barometer continued to fall 

 until 11 a.m., it" was then 28.892 accompanied by slight rain 

 (0-50 inch ;) the wind veered about noon by the N. to the W. S. 

 W., and increased to a velocity maximum 30-57 miles per hour, 

 which continued during the day following; wind W. X.- W. 



Electrical state of the atmosphere. — The atmosphere has 

 afforded indications of electricity, varying in intensity on every 

 day or nearly so, during the year, and was generally of a posi- 

 tive or vitreous character* Two remarkable electrical storms 

 occurred on the 23rd and 31st of December, indicating an inten- 

 sity of 450 - in terms of Volta's electrometer, No. 1 : sparks of 

 of ijtli of an inch were c nstantly passing from the conductor 

 to the discharger for several hours each day : it was of a posi- 

 tive character, with frequent and quick- changes to negative elec- 

 tricity. An increase of intensity is always observed during the 

 snow storms of our winter ; this increase generally possesses the 

 character of positive electricity, although frequent signs of nega- 

 tive electricity have been observed here ; this change from posi- 

 tive to negative electricity appears to be connected with change 

 in the form of crystals of snow.. The crystals of snow in this 

 climate daring the very severe weather, are generally those des- 

 cribed by Scoresby, and figured from 16 to 20 in Ka^intz's Me- 

 teorology, also fig. 3 ; and plain hexagonal prisms have likewise 

 been observed, 



St. Martin, Feb. 1, 18 S3. 



The Mississippi and Ohio Hi vers. 



From the Report by Charles Ellet, Jr., C. E. 

 The Mississippi. — To be able to form a just conception of the 

 present physical constitution of the delta, and the causes of its 

 overflow, we must imagine a great plane sloping uniformly from 

 the mouth of the Ohio, in a direction deviating but little from 

 a due southerly course, to the Gulf of Mexico. The length of 

 this plane, from the mouth of this river to the waters of the gulf, 

 is 500 miles. Its northern extremity is elevated 275 feet above 

 the surface of the sea, and is there and every where neatly level 

 with low water in the Mississippi River. Its total decent, follow- 

 ing the highest surface of the soil, is about 320 feet, or at the rate 

 of 8 inches per mile. 



The breadth of this plane, near the mouth of the Ohio, in an 

 east and west direction, is froin thirty to forty miles; aud at the 

 Gulf of Mexico it spreads out to' the width of about one hundred 

 aud fifty miles. 



It is inclosed on the east and west by a line of bluffs of irregu- 

 lar height and extremely irregular direction. 



This plane, containing about 40,000 square miles, has been 

 formed in the course of ages from the material brought down 

 from the uplands by the Mississippi and its tributaries. The 

 river has therefore raised from the sea; the soil which constitutes 

 its own bed. It flows down this plane of its own creation, in a 

 serpentine course, frequently crowding on the hills to the left, and 

 once passing to the opposite side and washing the base of the 

 bluff which makes its appearance on the west at the town of 

 Helena. 



The actual distance from the mouth of the Ohio to the coast of 

 the gulf is, in round numbers, as stated, 500 miles. The com- 

 puted length of the Mississippi River, from its confluence with 

 the Ohio to the mouth of fie South-west Pass, is 1,178 miles; 

 and the average descent at high water foths of a foot, 3j inches 

 per mile. 



The course of the river is therefore lengthened out nearly seven 

 A 



hundred miles, or is moi-e than doubled by the remarkable flex- 

 ures of its channel ; and the rate of its descent is reduced by these 

 flexures to less than one-half the inclination of the plane down 

 which it flows. 



In the summer and autumn, when the river is low and water 

 is scantily supplied by its tributaries, the surface of the Mississip- 

 pi is depressed at the head of the delta about forty feet, and as 

 we approach New Orleans, twenty feet below the top of its banks, 

 It then flows along sluggishly, in a trench about 3,000 feet wide, 

 15 feet deep -at the head, and 120 feet at the foot, and inclosed by 

 alluvial and often caving banks, which rise, as stated, from 20 to 

 40 feet above the w 7 ater. 



But when the autumnal rains set in, the river usually rises un- 

 til the month of Ma}', when it fills up its channel, overflows its 

 banks, and spreads many miles over the low lands to the right 

 and left of its trace. This leads to another important feature in 

 the characteristics of this great stream. 



The Mississippi bears along at all times, but especially in the 

 periods of flood, a vast amount of earthy matter suspended in its 

 waters, which the current is able to carry forward so long as the 

 river is confined to its channel. But when the water overflows 

 the banks, its velocity is checked, and it immediately deposits the 

 heaviest particles which it transports, and leaves them upon its 

 borders ; and as the water continues to spread further from the 

 banks, it continues to let down more and more of this suspended 

 material — -the heaviest particles being deposited on the banks, and 

 the finest clay conveyed to the positions most remote from the 

 banks. The consequence is, that the borders of the river, which 

 received the first and heaviest deposits, are raised higher above 

 the general level of the plane than the soil which is more remote ; 

 and that, while - the plane of the delta dips towards the sea at the 

 rate of eight inches per mile, the soil adjacent to the banks slopes oft' 

 at right angles to the course of the river, into the interior, for five 

 or six miles, at the rate of three or four feet per mile. 



The Ohio. — This noble tributary rises on the borders of Lake 

 Erie, at an average elevation of 1,300 feet above the surface of 

 the sea, and nearly 700 feet above the level of the lake. The 

 plane along which this river flows is connected with no mountain 

 range at its northern extremity, but continues its rise with great 

 uniformity, from the mouth of the Ohio to the brim of the basin 

 which incloses Lake Erie. The sources of the tributary streams 

 are generally diminutive ponds, distributed along the edge of the 

 basin of Lake Erie, but far above its surface, and so slightly sepa- 

 rated from it, that they may all be drained with little labour down 

 the steep slopes into that inland sea. 



From these remote sources, a boat may start with sufficient 

 water, within seven miles of Lake Erie, insight, sometimes, of the 

 sails which whiten the approach of the harbor of Buffalo, and 

 float securely down the Connewango, or Cassadaga, to the Alle- 

 ghany, down the Alleghany to the Ohio, and thence uninterrupt- 

 edly to the Gulf of Mexico. In all this distance of 2,400 miles, 

 the descent is so uniform and gentle — so little accelerated by 

 rapids — that when there is sufficient water to float the vessel, and 

 sufficient power to govern it, the downward voyage may be per- 

 formed without difficulty or danger in the channels as they were 

 formed by nature; and the return trip might be made with equal 

 security and success with very little aid from art." 



Ka.ii, a Sousce of the JVitrogeu in Vegetation. 



M. Barral, from some analyses of rain-water collected at two 

 distinct spots in the grounds of the Observatory at Paris, during 

 the last five and six months of the past year, has shown us that, 

 the rain-water is there charged with nitric acid, ammonia, chlorine, 



