NATIVE MURIUM. 127 



In the wheel D, the same effect is produced by the 

 screws, e, e, &c. which are made alternately right and left 

 handed, and turn with equal motions, by means of the equal 

 bevil-wheels/,/, &c. fixed at their ends near the axis of the 

 wheel. Fig. V. is a section of the same. 



The wheel C, Fig. I. and II. is moved round the shaft d 

 by the pinion g^ on the axis of which is fitted occasionally a 

 winch. The screws of the wheel D, Fig. III. may be also 

 turned, by means of a winch applied to their projecting 

 heads /i, hy h. It is proper to notice that the number of 

 the screws must always be equal. 



Andrew Flint. 



Goswell Street y London. 



IX. 



Account of a Discovery of native Minium. In a Letter 

 from James Smithson, Esq. F.R.S. to the Right Hon, Sir 

 JosEEH Banks, K.B. P.R.S.* 



MY DEAR SIR, 



JL BEG leave to acquaint you with a discovery which I character and 

 have lately made, as it adds a new, and perhaps it may be habitudes of 

 thought an interesting, species to the ores of lead. I have ""^"^^ niinium 

 found minium native in the earth. 



It is disseminated in small quantity, in the substance of a 

 compact carbonate of ?inc. 



Its appearance in general is that of a matter in a pulveru- 

 lent state, but in places it shows to a lens a flaky and crys. 

 talline texture. 



Its colour is like that of factitious minium, a vivid red 

 with a cast of yellow. 



Gently heated at the blowpipe it assumes a darker colour, 

 but on cooling it returns to its original red. At a stronger 

 heat it melts to litharge. On the charcoal it reduces to 

 lead« 



* Philosophical Transactions for x8o6. 



