On Smelting of Lead. 371 



show the necessity of some alteration in ihe table of the 

 seciilar variation of the moon's mean distance from her 

 node, which (agreeably to the rule given by M. Laplace) is 

 deduced immediately from the secular variation of her mean 

 longitude. These remarks, however, are thrown out merely 

 as hints to those who are more conversant with, and better 

 informed on, the subject : and I regret that I have not more 

 tune to pursue the inquiry further. 



Such an alteration, as is here suggested, would some- 

 what vary the position of the route of the moon's umbra, in 

 all the eclipses which have been the subject of this paper; 

 hut, m none of them would it alter the conclusions which 

 have been drawn from thein, excejjt perhaps in the one 

 (September 30ih, 610 B.C.) which I have suppcvsed to be 

 that mentioned by Herodotus. In this particular case, the 

 path of the moon's umbra might, by such a correction, be 

 thrown so much further north as to prevent the eclipse be- 

 ing total in any part of Asia Minor. But still it would re- 

 main the only one that can be at all adapted to the account 

 given by Herodotus ; since there is no other that could 

 possibly be central in, or near, any part of Asia Minor from 

 the year 650 B. C. to 580 B. C. : a period which far ex- 

 ceeds the probable limits of time wherein this singular phae- 

 nomenon must have taken place, so as to be reconcileable 

 to any received system of chronology, 



November 1810. F. B. 



LXVn. jln Account of the Smelting of Lead. By 

 Mr, John Sadler. 



[Concluded from p. '282.] 



J. HE substances which are found to render the ores of lead 

 refractory, when mixed with them, are cawk, {sulphate of 

 laryteSi) black jack, {hlend or sulplmret of zinc,) sulphur, 

 {iron pyrites,) and silver, or copper, when they are con- 

 tained in the ore in larger proportions than usual. 



1 have always considered that these substances render an 

 ore refractory by the extra quantity of sulphur they bring 

 with them. I do not think the earth or metals alone would 

 produce any visible effect in the smelting ; and I am almost 

 confirmed in this opinion, by repeatedly observing the eflect 

 j)roduced by roasting the ore previous to stnelting; it works 

 more pleasantly, requires less lime and fuel, and gives a 

 better produce. 



The quality of the coals materially afTccts the working of 

 A a 2 the 



