

LO E. Loomis—Ckmir'thtiiHtn-s t<> MtUorology. 



n the rear. In the few cases in which there was a fall of 

 ■ In the front, there was generally a greater fall in 

 he rear; and when there was a rise of temperature in the 

 •ear, there was generally a greater rise in the front. 



In my former papers'l have given reasons which appear to 

 ne to indicate that the progress of a low center does not con- 

 sist in a drifting of the general atmosphere eastward, but is 

 •ather like a wave whose characteristic feature is a diminution 

 nt of the storm, and an increase of pressure 

 : rear. The qu tich is now presented for 



our examination is. what causes the barometer to fall on one 

 side of a storms center, and to rise on the opposite side? I 

 shown that it is only indirectly 

 that the rain-fall contribntes to this effect. The fall of the 

 in the motion communicated to the air, and 

 is due partly to the centrifugal force arising from the circula- 

 tion about a cinter, but mainly (in ordinary storms) to the 

 influence of the earth's rotation in deflecting a moving body to 

 the right. ]>y the precipitation of the vapor of the air and 

 the heat which is thereby liberated, the surrounding air is 

 drawn inward towards the region of precipitation ; but the 

 movement which this cause (ends to produce, is modified by 

 causes previously in operation. These causes consist mainly 

 in the existing distribution of pressure, temperature and hu- 

 midity, not only within the limits of the storm, but throughout 

 an extensive region surrounding it on all sides. Moreover air 

 has inertia, and when once set in rapid motion, it retains the 

 motion acquired until this is overcome by the resistances en- 

 countered. In" the case of a great winter storm, a system of 

 winds is set in rapid motion over an area fifteen hundred miles 

 or more in diameter. When a new force begins to operate 

 tending to impress a different movement upon this vast mass 

 of air, the effect must be, not th at which the last cause would 



pr KJuce it it operated alone, but that which results from a com- 

 bination of the last force with the preceding forces. This prin- 



ciple will assist us in detecting the influence of rain-fall in 



progress. We see from 

 'late I that the greatest precipitation of vapor generally took 

 lace about four hundred miles east of the low center; and 

 us precipitation developed ., |", m .,. which tended to divert the 

 ■mds eastward, while a cold wind from the north or north- 

 r est was pressing in on the western side, and increasing the 

 ressure in the rear of the storm. 

 The test of the correctness of this general explanation must 

 onsist in its successful application to each of the seventv-four 

 ases in the table on page 2. I have made this comparison and 

 onsider the results to be satisfactory with the exception per- 



