1834.] On the method of extracting Saltpetre, 182 



is about 70 feet and the end of it under the surf is fixed to cross 

 timbers to prevent its sinking; deep into the sand. —The water in the 

 .upright arm of the syphon is drawn every day to ascertain that it 

 flows freely. As the pipe is doubtless in a great measure filled with 

 sand, it follows that the water neither flows nor ebbs in the syphon 

 to its exact extremes, and therefore, that the rise and fall given in 

 the Tables must be considered rather under the truth.— In many 

 instances, the difference of high and low water is as much as 4 feet 

 3 inches and even 4 feet 6 inches. The beating of the surf affect- 

 ed the water in the pipe and the rod oscillated up and down at 

 each stroke, but this oscillation did not exceed half ox three quar- 

 ters of an iach in the highest surfs. 



The variation of mean level of the surface of the sea noticed 

 above (5th column) accounts for the rise of the water in the river at 

 Madras during the dry season. The sea on intering at the Ennore 

 Bar, when the Chepauk Bar is shut up, comes down the canal 

 from thence ; after the full and change, the water is observed to 

 rise for two or three days, in about as many days more, fails again ; 

 while however the daily operation of the Tides is not perceptible, 

 from the distance of the Ennore Bar. This rise and fall has at the 

 Wallajah bridge been frequently observed to be as much as 8 or 10 

 inches. 



It is possible that the sea water filtering below the sands may 

 aid this operation a little, but not much ; for the ditch of the Fort 

 -which is kept full by means of ihis filtering underneath the sea face 

 counterscarpe, is scarcely affected by this rise of the sea above al- 

 luded to no more than by the flowing and ebbing of the Tides 

 daily. 



VI. — Translationfrom a work by, M. M. Botte et Riffault, 

 detailing the method pursued in France, of extracting Saltpetre 

 from the soil, and of ascertaining the quality of Saltpetre by 

 Assay, Communicated by Lieutenant Colonel Napier. 



As natural mines of Saltpetre exist in France, it has long been 

 an object of primary importance with the Government to improve, 

 and increase the manufacture of that article, by the employment 

 of men of science to establish manufactories upon the best and 

 most economical principles, by which means the produce of Salt- 

 petre was doubled in four years. 



A prize of 4,000 Livres, was offered by the Academie of Science, 



