18 H. C. Hovey—Danger from Coal-dust in Mining. 
the differences between the numbers in columns 4 and 9 for 
those stations whose heights have been determined by direct 
measurement, we shall find that the sum of the positive differ- 
ences is about equal to the sum of the negative differences, 
which seems to indicate that Guyot’s Tables give better results 
than Williamson’s erie and that they may be depended apor 
for heights deduced from the mean of a long series of baro 
metric observations. 
Stations of the U. S. Signal Service whose elevation above the sea 
is more th et. 
than 1,000 
Ee ban ee Ea 
Temperature. Elevation. 
Station Lat. | Long,|Elevat'n| Mean é Barom. 
if E "| Sig, Ser.) Barom Sea-lev. 
Station.) Sea-ley Laplace. Plant’r. 
Pike’s Peak__} 38°8 105° 0| 14150 | 17°750| 19°2 | 55:4 | 30-032) 14054) 14116 
Santa Fé --_-| 35°7 |106°2) 6851 ! 23-265| 48°8 | 58°8 | 30°023) 7011| 7029 
Mt, Washing’n| 44°3 | 71°3} 6285 | 23-626) 25°9 | 45°5 | 29-973) 6286| 6319 
. oe +2, 3 
Salt Take City] 41:2 |112'0| 4362 | 25°642| 52:4 | 53°3 | 30°042| 4342| 4355 
innemucea-j| 41-0 }117°7) 4335 | 25°621| 50°2 | 54:1 | 30°050| 4366] 4379 
Boise City...| 43°7 |1 877 | 27-144) 52:4 | 52-4 | 30°060} 2795) 2804 
North Platte_|41°1 |100°9| 2838 | 27°057| 48:7 | 51-7 | 30°029| 284i | 2851 
ity ..| 37°61 486 | 27°381| 54:1 | 56°6 | 30°033) 2549) 2557 
Bismark ___.- 8 |100°6) 1704} 28154) 41-0 | 42°7 | 30°010) 1708) 1716 
Yankton ._.-|42°7} 97-5) 1275 | 28°718| 45°8 | 49°5 | 30-023) 1205] 1208 
Port: Si oa. 34°7| 98°5 1100] 28779 60°6 | 60°6 | 30032) 1188] 1192 
Omaha ....-. 3| 96°0 1077} 28°876! 49°8 | 50°8 | 30-030} 1068) 1072 
In preparing the materials for this article, I have been as- 
sisted by Mr. Henry A. cogent a graduate of Dartmouth Col- 
ege of the class of 1871; r. Orray T. Sherman, a 
iT. 
Art. Il.— Coal Dust as an element of danger in Mining ; by 
Rev. H. C. Hovey, A.M. 
CHEMICAL action is often induced in heaps of slack, such as 
exist in thick coal workings, and the heat evolved may be 
enough to cause ignition. The danger is greatly increased 
when the broken coal is comminuted and floats in the air in 
the form of ey which under various soit doae may undergo 
rapid oxi atio 
Galloway’s experiment show that when the particles are so 
fine as to pass through the gauze shield of a safety-lamp, an 
explosion may be caused by t eir ignition. Bauerman states 
that in the French collieries, “several fatal a Na have 
been traced to the firing of coal dust from the flame of a blast, 
4 
