WEATHER-PROGNOSTICS. 653 



We should then have two cyclones, diflfering in nothing but depth ; 

 that is, in the closeness of the isobars, or the steepness of the baromet- 

 ric slope. Observation has shown that under these circumstances the 

 general character of the weather and the direction of the wind every- 

 where would be the same ; the only difference would be that the wind 

 would blow a hard gale in the first and only a moderate breeze in the 

 second case ; and that what was a sharp squall in the one would be a 

 quiet shower in the other. This is one of the fundamental principles 

 of synoptic meteorology — that the character of the weather and direc- 

 tion of the wind depend entirely on the shape of the isobars, while the 

 force of the wind and intensity of the character of the weather depend 

 only on the closeness of the isobars. 



The difference in the details of the weather in a cyclone, or any 

 other isobaric shape which are due to difference in the steepness of the 

 isobars, is called a difference in the intensity of the weather. Plence, 

 when we speak of a cyclone as being intense, we mean that it has 

 steep isobars somewhere. When we come to talk about the general 

 sequence of weather from day to day, we shall find that there is no 

 difference heticeen the cyclones which cause storms and those ichich 

 cause ordinary weather except intensity. This is another of the funda- 

 mental principles of meteorology. 



Returning now to our cyclone, the whole of the portion in front of 

 the center facing the direction toward which it moves is called its 

 front, and the whole of this portion may obviously be divided into a 

 right and left front. The other side of the center is, of course, the 

 rear of the cyclone. Then, as the whole cyclone moves along its 

 course, it is evident that the barometer will be falling more or less at 

 every portion of the front, and rising more or less everywhere in 

 the rear, so that there must be a line of places somewhere across the 

 cyclone where the barometer has touched its lowest point and is just 

 going to rise. This line is called the " trough " of the cyclone, be- 

 cause if we look at the barometer-trace at any one place, the " ups " 

 and " downs " suggest the analogy of waves, so that the lowest part 

 of a trace may be called a " trough." Or we may look at the cyclone 

 as a circular eddy, moving in a given direction, and so far presenting 

 some analogy to a wave. 



So far for the shape and names of the different portions of the 

 cyclone. Now for the wind. A glance at the arrows will show that, 

 broadly speaking, the wind rotates round the center in a direction 

 opposite to the motion of the hands of a watch. That is to say, that 

 in the extreme front, following the outer isobar, the wind is from the 

 southeast ; farther round, it is from the east-northeast ; still farther, 

 from the north-northwest ; then from about west ; and, finally, from 

 the southwest. Then we note that in front the wind is slightly in- 

 curved toward the center, and therefore blows somewhat across the 

 isobars, while in rear it has little or no incurvature, and blows nearly 



