November 15, 1901.] 



SCIENCE. 



157 



cupying waters. If one take a number 

 of chemical solutions in the laboratory, 

 and dump them together in a beaker, 

 probably precipitation will occur. These 

 conditions are precisely those of under- 

 ground solutions in trunk channels. The 

 water from one source meets the water from 

 another source in the trunk channels. An- 

 alyses show that waters from different 

 sources have different compositions. They 

 bear different metals and precipitating 

 agents. When they come together in the 

 trunk channels, and mingle, precipitation 

 is likely to take place. You, who are 

 practical mining men, like your veins to 

 intersect, or two veins to unite. The ex- 

 planation of the frequent increased values 

 at or adjacent to an intersection is simply 

 that the different trunk channels bear 

 solutions of different kinds, and when 

 they mingle at or near the intersections, 

 ore precipitation is likely to occur. One 

 solution may bear its mite of silver or 

 gold, and the other the precipitating agent, 

 or both solutions may carry the metals, 

 and when the two come together the 

 ore be thrown down. However, this is 

 not the only way in which precipitation 

 may take place. In many instances the 

 precipitation is due to the wall rock. The 

 wall rock, or the solutions furnished by 

 it, react upon the solutions coming from 

 somewhere else, and precipitation occurs. 

 These two causes for precipitation are not 

 the ones which are ordinarily mentioned 

 in treatises on ore deposits. The causes 

 commonlj'^ assigned in text-books for pre- 

 cipitation are the diminishing temperature 

 and pressure of the rising solutions. While 

 these are real causes for precipitation, I 

 believe them to be subordinate to the in- 

 fluence of the mingling of solutions from 

 various sources in the trunk channels, to the 

 influence of the wall rocks, and especially 

 to the first. C. E. Van Hise. 



( To be concluded. ) 



THE PHYSICAL SCIENCES AT THE BRITISH 

 ASSOCIATION. 



The meeting last September at Glasgow, 

 which was attended by nineteen hundred 

 persons, was smaller than the last two meet- 

 ings held in that city, and fell slightly 

 below the average of the British Association 

 gatherings. This was chiefly the result 

 of the unexpectedly small number of local 

 associate members enrolled, accounted for 

 by the fact that an International Exhibition 

 with several collateral congresses had satis- 

 fied whatever desire the inhabitants of the 

 Scotch metropolis may have had to increase 

 their knowledge of scientific matters. The 

 foreigners numbered only twenty- one, but 

 some who might have attended this meeting 

 had already been in Glasgow early in the 

 summer as delegates to the jubilee celebra- 

 tion of the University. Since the president 

 of the Association this year is one of the 

 most distinguished physicists in Great Brit- 

 ain, it was natural to expect a large gather- 

 ing of workers in his branch of science, but 

 here also certain well-known names were 

 missed from the list of members, which may 

 likewise be attributed to the above cause. 

 The meetings of all the sections were very 

 conveniently held in the splendid Univer- 

 sity buildings on Gilmore Hill, the Physical 

 Section holding its sessions in the Natural 

 Philosophy Class Room, rendered famous by 

 Sir William Thomson, now Lord Kelvin. 

 The only criticism that could be made of 

 the local arrangements was the absence of 

 notices at the doors of each section indicat- 

 ing what paper was being read, but the 

 same complaint has frequently been heard 

 at our American Association meetings. 



Professor Riicker's presidential address, 

 which has already appeared in Science, was 

 a scholarly defense of the atomic theory of 

 matter, but some disappointment was mani- 

 fested that the objections of its opponents 

 were not definitely stated. Lord Kelvin 

 who seconded the vote of thanks to the 



