292 



EECREATIYE SCIENCE. 



perfectly-crushed ore, a signal is given ; it is 

 hauled up to undergo a repetition of the 

 process ; and this is continued until the whole 

 is reduced to an uniform condition of fineness. 



Even now, notwithstanding the sorting 

 process, a very considerable amount of quartz 

 remains intermixed with the crushed ore, and 

 as this would very much interfere with the 

 subsequent smelting, it becomes necessary to 

 remove it. In order to understand the prin- 

 ciple upon which the operation next to be 

 described is based, the reader must remem- 

 ber that galena is very much heavier than 

 quartz ; and that, supposing a mixture of two 

 substances, one heavy and the other light — as 

 sand and shot, for example — to be thrown 

 into a running brook, the sand would be 

 carried to some distance by the water, while 

 the shot would remain almost at the place 

 where it was thrown in. 



It is by taking advantage of this diffe- 

 rence in specific gravity, that the separation 

 of the galena from the " gangue," as it is 

 called, is effected. After passing from the 

 sieve, the crushed ore meets in the gutter or 

 channel with a stream of water, which, hav- 

 ing already turned the water-wheel, is fur- 

 ther made to wash the ore, and still come 

 along pretty rapidly and with some force. 

 Very soon the effect of its action is made 

 manifest. At intervals along the water- 

 course are lateral openings into shallow 

 tanks, and here are stationed men, armed 

 with instruments like a rake minus the 

 teeth, who draw into the reservoirs the ga- 

 lena which accumulates in the channel. To- 

 wards the upper extremity of this simple 

 washing apparatus, are found lumps of ga- 

 lena ; but as we go lower down, we find that 

 these diminish in size, until, having degene- 

 rated into a mere plumbeous sand, the lead 

 ceases altogether, and in its stead we come 

 upon nothing but the rejected quartz, the 

 particles of which, in the same manner, grow 

 small by degrees, and finally dwindle into 

 dust. At the upper part, where the galena 



lies in small lumps, we find quartz in rather 

 larger fragments, which have resisted the im- 

 pulse of the stream, and remain intermixed 

 with the ore. This portion is reserved for 

 treatment in a series of oblong boxes, which 

 have a jerking motion communicated to 

 them. These boxes are filled with the 

 mixed ore and qiiartz, and in the same way 

 as shaking a basket of chips and halfpence 

 would determine the subsidence of the latter 

 to the bottom, does the galena separate itself 

 from the less heavy quartz, which is removed 

 from time to time to make room for a new 

 supply. When removed from the washing- 

 tubs, the galena is placed in heaps, each of 

 which is the share of a miner. With the 

 correct weighing and transference of the ore 

 to long cofiin-shaped boxes, in which, securely 

 padlocked, it is conveyed to the smelting- 

 works, the mechanical part of its treatment 

 ends, and it bids farewell to the mine. 

 Dublin. Haeey Napibe Deapee. 



STAE SCINTILLATIONS. 

 •«• 

 We are informed by Humboldt, that in the 

 tropics the stars shine with a steady lustre, 

 not twinkling or scintillating as they appear 

 in our zone. The cause of this appears to me 

 very simple, and I will proceed to explain it. 

 Between ourselves and the stars there are 

 many atmospherical strata of various densi- 

 ties, which diversity in density of strata 

 may perhaps extend to the ether beyond the 

 limits of our atmosphere, if such exists. It 

 appears that this diversity of density causes 

 the apparent twinkling of the stars, because 

 we find the same phenomena in connection 

 with terrestrial objects. If we look at a gas 

 jet at a distance, it will appear surrounded 

 with scintillations, which are not seen if 

 we are close to it. These are more appa- 

 rent when the weather is foggy, because 

 the diversity in the densities of the strata is 

 then greatest. J. A. Davies, 



