Proceedings of the Polytechnic Association. 9G7 



that concentration may be advantao-eously nsed in the treatment of 

 the tailing-, etc. The important feature of tliis machine is the a})})]i- 

 cation of putfs of air to the powdered ore. There have ])een other 

 machines whicli work by straight currents of air. A gh)be of quartz 

 and another of lead, if allowed to pass through water, will both reach 

 the bottom at the same time. This is not so when the particles are 

 reduced and passed tlirongh l>lasts of air, as when the ore is very 

 fine it passes very slowly. The cost of a full size machine is s50<.». 



Mr. Alanson Nash said that the tine gold that is f >und in the 

 earth, when put into a rocivcr, often has that degree of lineness that 

 the water will carry it down in the -rocker, where it will be scattered 

 away; so if very tine gold dust is subjected to puffs of air, much of 

 it Avill be blown away. A metal so valuable as gold should all be 

 saved, and hence the fanning process did not seem to l)e a good one. 



Mr. Ilandall stated that water becomes turbid if shaken with gold 

 dust in it, and it will stand f)r lioui-s in that condition without settle- 

 ing. The pans used in California are the best method for gathering 

 the gold if mercury is used. In the treatment of silver ores, concen- 

 tration is not advisable. » 



The Gulf Stream. 

 Pr(.)f. T. B. Maury spoke at some length on this subject, illustrating 

 his remarks by frequent reference to large maps which he had ju'o- 

 vided. lie said the subject on which he was to speak, M-as the great 

 oceanic current known to geographers as the gulf stream. When 

 Christopher Columbus crossed the Atlantic, he fell in with the cele- 

 brated trade winds, whicli connnenced at the Tropic of Cancer, and con- 

 tinued in one unbroken belt across the wliole earth, twenty-three degrees 

 north of the ecpiator, and thirty degrees south of it. It was in this 

 portion of the belt that Cubnnbus iirst met these trade winds. He 

 found that day after day the wind continued to blow in one direction ; 

 and blowing as they do, I infer they carry \vith thcni a lai-go portion 

 of the surface waters of the Atlanric, and sweep them to the west, 

 lie also foimd that a large portion of tlu; waters of the Atlantic follow 

 the sun, moon ;md stars. Tlu.'se waters are swept up again>t the Wind- 

 ward isles, where it is sjdit in two ; a ])art known as the gidf .■stream, 

 passing through the grou}i of islands into the Caribbean sea; thence 

 making the circuit of the (iulf (^f Mexico, passing up the coast to a point 

 opposite Cape Ilatteras, ainl then striking out to the western coast of 

 Europe, and again nortliwai-dly along the fScandimivian coast into the 



