On the Nautical Ephemeris. 215 



ferent springs. The brine being piimpeil out of the pits, 

 is first conveyed into large reservoirs, and afterwards drawn 

 off as it is wanted, into evaporating pans, made of wrought 

 iron. Here heal is apphed in a degree determined by the 

 nature of the salt intended to be manufactured, and various 

 additions are made to the brine, with a view either to assist 

 the crvstalhzation of the muriate of soda, or to promote 

 the separation of Uie earthy salts. The latter exist in a very 

 small proportion in the manufactured salt, and cannot be 

 supposed in any degree to affect the uses to whicft it is ap- 

 plied *. The importance of the Cheshire salt manufacture 

 will be sufficiently obvious from the statement, that besides 

 the salt made for home consumption, which annually 

 amounts to more than 16,000 tons, the average of trie 

 quantity sent to Liverpool for exportatiou has not been less 

 than 140,000 tons. 



[To be continued.] 



XXX I. On the Nautical Ephemeris, 



To Mr. Tilloch. 



Sir, a. great deal having lately been written and said 

 about the error in the Nautical Ephemeris for 1812, but 

 very little towards assisting the public in correcting this 

 trifling mistake, I flatter myself some of your readers will 

 not be displeased at having an easy and expeditious mode 

 of correcting the Sun's Declination as given in the Ephe- 

 meris ; this being The part most affected by having as- 

 sumed an erroneous apparent obliquity of the ecliptic in 

 the calculation of that work. 



The following small table of corrections I do not claim 

 as my ov/n ; I found it in the Connoissauce des Terns for 

 1812, where they also give the formula of its construction. 



The correction is for every third degree of declination, 

 and for one second of difference in the real and assumed 

 obliquity of the ecliptic. All that is requisite to the appli- 

 cation of the following table is to multiply the tabular 

 number by the difference between the real and assumed 

 obliquity. 



The difference between the real obliquity and that as- 

 sumed in the computation of the Ephemeris for 1812, is 

 supposed to be about b" too little, 



* Id reference to the chemical character of the dilTcrent varieties of salt, 

 an excellent paper by my friend Dr. Henry will be found in tlie Pliilosophi- 

 cal Transactions for the year 1810, pajt i. 



4 Tablk 



