CLIMATOLOGY OF NEW HAMPSHIRE. 121 



rises, thus creating an area of low pressure, which is the nucleus of the 

 storm area that is carried eastward across the continent. The other 

 great storm-centre is within the tropics. The great current of the south- 

 east trade-wind infringes on the north-east trade-wind, and produces the 

 cyclones that are so destructive in the West Indies and on the coast of 

 Florida. The cyclone thus generated moves along our coast, generally 

 with greatly diminished force, and thus we have our north-east storms. 

 The character of these storms was first pointed out by Franklin, and 

 the theory as to their origin has been discussed by Espy, Redfield, 

 Maury, and others, while Prof. Joseph Henry was the first to explain the 

 origin of the storms that move eastward across the continent. In sum- 

 mer, the disturbances seem to originate chiefly in the vicinity of the 

 Rocky Mountains, while in spring, autumn, and winter, frequently, they 

 have their origin within the tropics. 



From the observations of the Signal Service, we find that there are 

 from seven to thirteen areas of low barometer developed per month 

 within, or pass along the border of, the United States. Of these, from 

 one to three pass directly across or along the border of New Hampshire. 



WEATHER MAP. 



The weather map on the opposite page shows graphically the tracks 

 of the storm-centres for January, 1874. It will be seen that two of the 

 storm-centres passed directly across New Hampshire ; and it will also be 

 seen that the storms, as a whole, are chiefly of the type that have their 

 origin in the vicinity of the Rocky Mountains. The dotted line from the 

 Pacific coast indicates only the probability that the storm-centre passed 

 over that section of the country. The storms from the south usually pass 

 along or nearer the coast than the one represented on this map. By trac- 

 ing each storm-centre, a person can get some idea as to the probability of 

 the Signal Service being able to give accurate forecasts of the weather. 

 On account of our high latitude, sea border, our lofty mountains and nar- 

 row valleys, for our limited area the climate is exceedingly varied. On 

 the coast, the cold of winter and the heat of summer are moderated by the 

 breezes of the ocean. Inland, for a very few days in summer, we have 

 more than the heat of the tropics ; while on our highest mountain sum- 

 mits in winter, we have the climate of Greenland, if anything, more 

 VOL. i. 1 6 



