B. TERRESTRIAL PHYSICS AND METEOROLOGY. 73 



eral clays, descend half an inch or an inch during the next 

 two or three days, fire-damp may be expected in greater 

 quantity than usual. As the curve of temperature rises to 

 lifty-five degrees and upward, the ventilating power should 

 be increased at the same time, and the higher the temperature 

 the greater is the necessity for such increase, in order to pre- 

 vent, if possible, stagnation of the ventilating current. If a 

 sudden great fall of the barometer take place say, an inch 

 in twenty-four hours or a further fall after it has been un- 

 usually low for a day or two, the utmost care will be neces- 

 sary to guard against explosions, more especially if a rise of 

 temperature accompany the fall of the barometer. 



In conclusion, the opinion is expressed that the majority 

 of the explosions can be prevented by good ventilation. Fire- 

 damp would be almost unknown in many mines with a plen- 

 tiful unvarying supply of air introduced and properly distrib- 

 uted. The observations indicate that, in order to confine the 

 chances of explosions within the narrowest limits, it will be 

 necessary to introduce an instrument that shall keep a con- 

 stant record of the whole ventilating power employed, nat- 

 ural and artificial. Quar. Jour. Meteor. Soc. t 1873, 246. 



THE WEATHER OF DECEMBER, 1873. 



The monthly weather review of the Army Signal-office for 

 December gives the details of twelve storms, of greater or 

 less severity, that have prevailed within the limits of the 

 net-work of stations maintained by the United States and 



ml 



Canadian governments. Two of these storms started from 

 the northwestern portion of the Gulf of Mexico, and passed 

 along the Atlantic coast to the eastward of Nova Scotia. 

 Four started from Western Texas, and passed northeast- 

 ward over New England and Canada. Six came from the 

 extreme Northwest, and passed nearly eastward over the 

 Lake region. Of all these storms, that which passed over 

 Kansas on the 2d of December, and moved thence over Lakes 

 Michigan and Huron, was by far the most severe. It was 

 accompanied with snow from the Lake region westward to 

 California, with unusual cold. On the 1st of December, prob- 

 ably in connection with the storm, a heavy sand-storm was 

 reported at Yuma, New Mexico. There were hoisted at 

 American ports sixty-three cautionary signals, and for Cana- 



D 



