376 On the Error discovered in the Nautical Almanac. 



which floats on the surface of the lead, ami which, being as 

 liquid as lead, might otherwise flow out along with it. The 

 slag being thus thickened \i\ an admixture oT" lime, is raked 

 up towards the sides ot the lurnace, and the lead is left at the 

 bottom. There is a hole in one of the sides of the furnace, 

 which is properly stopped during the smelting of the ore; 

 when the slag is raked off, this hole is opened, and being 

 situated lower than the lead in the furnace, the lead gushes 

 through it into an iron pot placed contiguous to the side ot the 

 furnace; from this pot it is laded into moulds, each con- 

 taining what they call a pig of lead : the pigs, when cold, 

 being ordinarily stamped with the maker's name, are sold 

 under the name of ore lead. After the lead has all flowed 

 out of the furnace, thev stop up the tap-hole, and drawing 

 down the slag and lime into the middle of the furnace, 

 they raise the fire till the mixture of slag and lime, which 

 they term simple slag, is rendered very liquid; upon this 

 liquid mass thev throw another quantity of lime, to dry it up, 

 as in the former part of the process. This second mixture 

 of slag and lime is then raked out of the furnace, and the 

 small portion of lead separated from the fusion of the first 

 generally to the amount of twenty or thirty pounds, being 

 let out of the furnace, a new charge of ore is put in, and 

 the operation recommenced. In order to spare the lime and 

 the expense of fuel attending the fluxing of the mixture of 

 lime and slag, they have in. some furnaces lately contrived a 

 hole, through which they suffer the main part of the liquid 

 slag to flow out, before they tap the furnace for the lead ; 

 upon the little reniaininff slag they throw a small portion of 

 lime, and draw the mixture out of the furnace without 

 smelting it. This kind of furnace they have nick-named 

 a maccarcni." 



LXVIII. On the Error discovered in the Nautical Almanac, 

 By Mr. Firminger, late Assistant at the Hoyal Ob' 

 strvatory, Greenwich*. 



To Mr. Tilloch. 



Sir, In your journal for the last month, your readers will 

 doubtless notice, with much surprise, an account of an error 

 in the Nautical Almanac for the year 1812, which is therein 

 said to have bce-i recently discovered by Dr. Kelly. To re- 

 move, however, from the minds of such readers and others, 

 whom this circumstance may happen to interest, the mis- 



• Teaclxr of Anronomy, Mathematics, and the various branches of 

 Nalural Pl.ilosophy. 



take 



