NATURAL HISTORY OF GENEVA. 1 G9 



made a more complete examination of the facts. He observed the sud- 

 den variations at the two extremities of the hike, and in the interme- 

 diate station of Morges, where they are less sensible. The duration of 

 one of these sucUlen changes varies little in each locality, but differs 

 much from place to place. At Geneva it is 1,590 seconds ; at Veytaux, 

 near the eastern extremity, 1,783 seconds ; and in the middle, at Morges, 

 2C4. This latter locality presents a rhythmic movement of 22 seconds. 

 M. Forel compares these movements of the lake to those of water in a 

 basin, in which the height and duration of the waves of oscillation de- 

 pend upon the form of the vase and the depth of the liquid.* 



The soundings of M. Forel at diiferent depths i)roved to him the 

 existence of three strata at the bottom of the hike: 1st. An upper 

 stratum of yellowish silt, containing a large number of animals, living 

 and dead. 2d. A stratum of about 4 inches of black clay. 3d. A lower 

 stratum of blue clay, very fine and very homogeneous, except near the 

 mouth of the Ehone, where it contains some mica. 



M. Raoul Pictet profited by his sojourn in Egypt to study more accu- 

 rately than had yet been done the water of the Nile. His principal 

 oi)eratious of gauging took })lace near Cairo, at the bridge of Kasr-el- 

 Nil. He sounded the river from shore to shore at 38 points, 33 feet 

 distance from each other. The velocity was measured by means of 

 the apparatus of Woltmann. The lowest water occurs about the 15th 

 of ]\Iay ; the amount of water there is 24,000 cubic feet a second. The 

 highest water is on the 15th of September, the amount then being 

 372,000 cubic feet. The mean is 108,000 cubic feet a second. The 

 greatest velocity 3 feet below the surface is G feet 9 inches ; the least, 

 7 inches. 



M. Pictet has frequently observed the sand spouts, which are a daily 

 phenomenon on the plains of Egypt. About 10 o'clock in the morning, 

 the sun having heated the surface of the ground, there results in the 

 adjoining stratum of air an ascensional and gyratory motion, which 

 carries up sandy particles to a height of 5,000 to 0,500 feet. Tlie cen- 

 tral part of the column has a temperature of from 45^' to G0<^, that of 

 the atmosphere in the shade being from 25° to 35°, centigrade. 



Prof. A. Gautier i)resented an article upon the therraometric obser- 

 vations made at Labrador by some Moravian missionaries. They form 

 a continuation of those presented in 1870. 



Geology. — Prof. Alph. Pavre has regularly informed the society of the 

 condition of the labors of the Swiss Geological Commission, of which 

 he is a member. The geological chart of nroVoo ^^ published in eleven 

 sheets, with five sheets of especial charts, concerning the canton of Bale, 

 tlie environs of Brugg, Mount Pilatus, the St. Gothard, and the Sentis, 

 (in two sheets.) The commission moreover has been especially occu- 

 pied on the St. Gothard, where the great work of forming a tunnel 



* Forel upon the seiches in the Bulletin of the Soc. Vaudoise des so. nat., 1S73, p. 213 

 and Archives of the so. phys. and uat., January, 1874. 



