28: 



Diameter. 



iU 



1 



5"(T 





Touo~o 



Terminal Velocity in feet per second 



. 11.86 

 10.27 

 . 9.182 



6.498 

 . 2.055 



1.453 

 . 1.027 



0.647 



Assuming the thickness of the vesicle to be a very small 

 fraction of its diameter, the terminal velocity will be simply 

 proportional to the square root of the thickness. Thus a vesicle 

 say xnW of an inch in diameter, and ^-0-0:000 of an inch thick 

 will have a terminal velocity of 0.5034. If the thickness be 

 T.TjW.TT^tr inch, the terminal velocity will be 0.1591 feet per 

 second, or about ten feet per minute. 



Prof. Rogers also exhibited specimens of Iron ore and 

 shale and shaly sandstone, more or less impregnated with 

 Proto-Carbonate of Iron, from the Bituminous Coal region 

 of the Trans-Alleghany basin, and called the attention of 

 the Society to what he regarded as the most probable and 

 simple theory of the origin and accumulation oftheProto- 

 Carbonate of Iron in coal measures generally. 



This compound of Iron, as we know, where mined in the coal 

 measures, presents itself in courses of lenticular nodules and 

 interrupted plates usually included in carbonaceous shales and 

 in the fire-clays which underlie the seams of coal, and in such 

 cases it often forms a heavy ore containing but little earthy or 

 organic matter mixed with the Proto-Carbonate. But it is also 

 frequently met with in a diffused condition^ pervading thick strata 

 of shale and shaly sandstone, and causing these rocks to present 

 in their different layers all the gradations of composition, from a 

 poor, argillaceous and sandy ore, to beds of sandstone and shale, 

 with little more than a trace of the ferruginous compound. 



On comparing the different subdivisions of a system of coal 



