Polytechnic Association Proceedings. 665 



5. Causes operating during gestation, through the excited ima- 

 gination or nervous sensibility of the mother. 



6. Ill health of the mother during gestation, or physical accident 

 during that period. 



7. Intemperance in one or both parents about the time of con- 

 ception. 



8. The influence of unhealthy occupations, bad water, inferior 

 diet, or damp dwellings of the pai*ents, on their offspring. 



9. Direct hereditary transmission. 



All these primary causes, the intelligent reader will see, are, 

 mutatis mutandis, as applicable to other congenital infirmities, as 

 well as to deaf-dumbness. A defective bridge gives way at its 

 weakest point; and where there is no specially weak point, the 

 point of fracture may be determined by slight causes. So it seems 

 there are families in which the weak point of the constitution is 

 the apparatus of hearing; but in many cases the tendency to deaf- 

 ness, rather than to idiocy, blindness, lameness, or some other 

 infirmity, was biased by causes that often baffle research, because 

 they eeem so slight that they elude attention. 



TIN IN anssouEi. 



The reported discovery of numerous veins of tin ore in the 

 county of Madison, Mo., is causing great excitement among specula- 

 tors in mineral lands. If reports be true, we must regard this 

 discovery as one of the most important events in the history of 

 American mining. Tiu has long been sought for, but thus far the 

 few veins found have been too small to warrant their being suc- 

 cessfully worked. Some hopes Mere entertained that the vein at 

 Jackson, N. H., would be favorably developed. Ver}^ little tin 

 has, however, been found in that locality. At a later period it 

 was expected that tin would be found, in pa>nng quantities, on the 

 Pacific coast; yet no tin is now exported from California. Our 

 principal source of supply has been the Cornwall mines of Great 

 Britain, which yield about six thousand tons of tin annually. 

 Bolivia, South America, exports about three thousand tons; the 

 Island of Banca, in Asia, four thousand; the Peninsula of Malay, 

 one thousand; and Australia, one thousand. On the continent of 

 Europe, two mines are now opened in Bohemia, one in Saxony, 

 three in France, one in Sweden, and one in Siberia. These, as well 

 as the Spanish mines, which are as old as those of Cornwall, do not 

 yield a surplus for exportation. 



