456 METEOROLOGY. 



the middle of wbicli is marked by the greatest destructive effect of the 

 motion. 



u. The effects of the tornado at any one pUice are x^roduced in a very 

 short time. It passes over different points of its path with great 

 rapidity. 



4. It commences at a given place with a crash, and passes off as sud- 

 denly into a calm. 



5. The tornado, even the most violent, seldom lowers the barometer 

 but little, and sometimes produces no appreciable effect in this way. 



G. The tornado is generally accompanied with discharges of electricity, 

 with large quantity of rain falling in a few minutes, and frequently 

 with hail, (sometimes in two tracks, one on each side of the path of the 

 meteor.) 



Character of tempests according to the same author : 



1. Tempests are of great extent ; they are not accompanied by an 

 isolated cloud as is the case with the tornado, but with one of apparently 

 unlimited extent. 



2. Moderate tempests continue sometimes ten or twelve hours, while 

 the most violent ones in some cases continue thirty-six hours, with 

 slight intermissions in the greatest intensity. 



o. All tempests are connected with the falling of the barometer, even 

 to the extent in some instances of an inch and a half. 



4. The tempest does not come on suddenly', but manifests its approach 

 by a gradual fall of the barometer, and an increase of the velocity of the 

 wind. 



Eemaeks. — The fact stated in regard to the fall of the barometer in the 

 case of the tempest, and not in regard to the tornado, is very important 

 as bearing on the different characters of the two meteors. It would 

 ai)j)ear to indicate that the tornado is not only of limited extent horizon- 

 tally, but also in a vertical direction ; that it consists of a violent overturn 

 of two strata of different density, the one rushing upward through a cir- 

 cumscribed space, and the other descending probably around the same 

 space, so that the sum of the two pressures remains the same, while in 

 the case of the tempest the air rises over a large space, and Hows over 

 at the top of the atmosphere. — [J, H.] 



AtCOli\T OF A TOR\ADO WHICH OCCIKRED IN SPRUCE CREEK VALLEY, 

 CENTRE COUNTY, PENNSYLVANIA. 



By the Ekv. J. B. Meek. 



Spruce Creek Valley is situated in the Alleghany range, and extends 

 in a southwest and northeast direction between Tussey's Mountain on 

 the northwest and Bald Eagle Mountain on the southeast. My resi- 

 dence was in the bottom of this valley near the south side. The fore 

 part of the dwy on which the tornado took placft was very warm, moist, 



