262 



Chemical Society, tlie Franklin and Wilmington Institutes, 

 the Editor of the Rural Economist, the Minister of Public In- 

 struction at Santiago de Chili, and Mr. George Ord. 



Mr. Lesley described the super-anticlinal situations of the 

 more violent oil-springs of the West, on the authority of Gene- 

 ral Pomeroy, and stated that it is a law of our principal car- 

 boniferous synclinal troughs to have at least one subordinate 

 commonly excentric anticlinal in its floor, dividing it longitu- 

 dinally into at least two troughs, in each of which the salt 

 water collects. The principal collection of oil and gas, on 

 the contrary, takes place at the crest of the intermediate anti- 

 clinal, and the most violent explosions of gas issue from 

 borings along this axis. Professor Cresson illustrated the 

 structural law thus stated, by referring to the report of Pro- 

 fessor Faraday to the British Government on the explosions 

 of coal-gas in the English mines. These are particularly dan- 

 gerous in the vicinity of " inverted troughs," or anticlinals, in 

 the upper part of which the gas collects. Any unusual fall of 

 the barometer is of course the signal for a copious downflow 

 of fire-damp from these reservoirs, the pressure which keeps 

 it there being for the time taken oiF. The same pneumatic 

 law propagates originally slight or moderate explosions to 

 great distances along the workings. The first explosion, with 

 its corollary vacuum, sets free a volume of gas involved in the 

 goaf or gob of the neighborhood ; this, when exploded in its 

 turn, sets free fresh volumes of gas still farther on. 



Professor Cresson, alluding to the fact that much of the re- 

 flected light we see is polarised, whence the glare and difficulty 

 experienced regarding pictures and objects under glass, de- 

 scribed an application of the Nichols prism to the opera glass, 

 made by Dr. Charles M. Cresson, by which the difficulty is 

 successfully encountered, and objects can be read under glass 

 obliquely as plainly as when uncovered. 



The Society was then adjourned. 



