PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 341 



surface. TIic limits of velocity were from 15 to 20 seconds. These mca- 

 siiromcnts coincide with those of more recent observers. By diagrams 

 and apparatus the lecturer illustrated the light, color, duration, length, 

 position and direction of shooting stars. 



New Mode of Moving Organ Keys. 



In the organ for the Church of St. Augustin, Paris, a substitute is to be 

 used for the present cumbrous mechanism, which communicates motion 

 from the ke^'s to the pipes. Electricity is to be employed, and probably iu 

 a manner somewhat sin7ilar to that applied in looms for weaving. 



Coal. 



Prof Henry D. Rogers, now of the University of Glasgow, has lately 

 published a paper on coal and coal mining, from which it appears tliat the 

 extent of the coal fields of the United States is fifty times that of the coal 

 fields of Great Britain. According to Mr. E. Hull, about one-half of the 

 amount in the British coal fields has alreadj'' been consumed. That which 

 remains is the most inaccessible. Prof. Rogers, after quoting the state- 

 ment of Sir William Arstrong, that at the present rate of increase in the 

 annual consumption of coal, the entire quantity of available coal existing 

 in the British Islands will only last 212 3^ears- and alluding to the fact that 

 the temperature of the earth increases 1'^ Fahrenheit for every 60 feet of 

 progress downward, while for every 300 feet there is an increase in the 

 heat of the air of 1° he proceeds to show that it is possible towork mines 

 even to the depth of 4,000 feet by forcing into them condensed air, whicli 

 on expansion will absorb heat and pass rapidly upward through the shafts. 

 A modification of the French boring machine, which is operated by atmo' 

 spheric pressure, has been introduced into the mines. By this means the 

 compressed air forced into the mine is first made to perform the duty of 

 cutting coal, before it is used for ventilating purposes. Many of the veins 

 hardly exceed three feet in thickness. Thej'' are worked by the miner 

 when lying on his side in a very cramped position. In such veins this 

 ooal-cutting machine will be of great service. But Prof. Roger's, hopeful 

 statement does not relieve apprehensions with regard to the fate of England, 

 In his estimates of the present resources, coal to the depth of 4,000 feet is 

 included, yet at half that depth there is an increase of 40^ in the tempera- 

 ture, and labor could not be performed there without a supply of colder air. 

 Ad(| to this the increased cost of pumping water from the mine, the 

 increased danger of fire-damp, and we see obstacles sufficient to prevent 

 the working of coal mines below 2,000 feet. 



Mr. Joseph Dixon remarked, in rcdation to the feasibility of using atmo- 

 spheric power at great depths, that l^e remembered reading an account of 

 an attempt to work a cylinder-bellows at an iron furnace in Wales, by 

 means of a powerful waterfall one mile and a half distant. The conducting 

 pipe was of great diameter, air-tight, and smooth within, yet the air forced 

 through it would hardly blow out a candle. An account of this experiment 

 may be ft^und in the Franklin Journal, Vol. IX., p. 147. 



