STOCKS: "COAL BALLS" AND " BAUM POTS." 395 
by such water percolating- through the rock, and be carried by it 
into the coal, where the carbonate of lime would deposit round some 
stem or other part of a plant, thus forming a coal ball ; the phosphate 
of lime being left with the decomposing shells, which would them- 
selves become gradually covered by carbonate of lime from the 
surrounding shells, and in time form a " baum pot" which would 
contain most of the phosphoric acid of the shells, thus accounting for 
the presence of it in greater quantity in the " baum pots" than in 
the " coal balls." 
The amounts of silica and alumina are also larger in the " baum 
pot" than in the "coal balls," this would seem to show that the 
carbonate of lime in forming the "baum pot" had enclosed some of 
the shale, which did not occur in the formation of the "coal balls." 
ON THE FIEE-DAMP DETECTOR, WITH EECENT IMPROVEMENTS 
IN THE MINERS' SAFETY LAMP; AND SOME REMARKS ON 
THE DIFFICULTIES CONNECTED WITH DEEP MINING. BY 
W. E. GARFORTH, C.E. 
The early history of the safety lamp is, that in the year 1815, Sir 
Humphrey Davy and George Stephenson, the celebrated railway 
engineer, unknown to each other, invented the lamps known by 
their respective names. 
It is generally admitted that Dr. Reid Clanny, of Sunderland, 
first conceived the idea in 1813, but as his lamp was dependent upon 
a supplementary appliance, and not on the surrounding atmosphere, 
the credit is given to Davy and Stephenson, both of whom received 
pubhc recog-nition for the invention. 
The safety of the Davy lamp is based on the principle that a 
flame in passing through a metal gauze of a certain mesh (the 
standard at present is about 784 apertures to the square inch), loses 
so much of its heat as to be incapable of igniting the explosive 
atmosphere surrounding it. 
