294 On the Elevation of the BanJcs of the Mississippi. 



will consequently enter at E and water escape at C, thus the water 

 in the filter will be kept at the level required. The pure water that 

 issues at C displaces the solution below it, and the washing goes on 

 in the most rapid and best manner possible. 



Gay-Lussads arrangement is equally simple, and may be pre- 

 pared with even more facility than the preceding. The water is 

 contained in a wide mouthed bottle AB (Fig. 4.) which is closed by 

 a cork, through which passes a syphon with equal legs (CD) and a 

 strait tube EF, whose lower orifice is a little above the level of the 

 opening of the syphon. To facilitate the entrance of the air by 

 means of this tube, it is cut off obliquely at bottom, as shown in the 

 figure. The end D of the syphon being plunged into the liquid in 

 the filter, the water will commence running cut, while air enters, 

 bubble by bubble, through the tube EF. The watisr in the filter 

 will not rise above the level of the orifice F. 



The best shape of the syphon is shown in Fig. 5. in which the 

 exterior opening is turned upwards. No practical chemist should 

 be without one or the other of the above arrangements. 



Abt. XVII. — On the Elevation of the Banks of the Mississippi, 

 in 1811; by F. C. Usher. 



Princeton, (N. J.) July 20, 1836. 



TO PROP. SILLIMAN. 



Dear Sir — Having failed, while I was in New Haven, to comply 

 with your request, that I should give to you on paper those state- 

 ments that I made to you in the lecture-room, respecting the eleva- 

 tion of the banks of the Mississippi by the earthquakes of 1811, I 

 will take the privilege of doing it now and sending it to you. 



The statements which I shall make, I learned from the inhabitants 

 of that place, together with what I saw myself. But having taken 

 no notes, my memory being treacherous at that time, from ill health, 

 and several years having elapsed since I was there, my statements 

 will, of course, be liable to incorrectness. Notwithstanding, they 

 shall be as near the truth as I can make them. 



That you may the better understand my statements, I send with 

 this as correct a map of the river there, as I can prepare. 



In the fall and winter of 1811, (I believe,) those earthquakes took 

 place. Their center was Madrid and Madrid bend. On both sides 



