518 Mr. J. A. Broun on the Directions ^c. of [Feb. 1^ 



Table III. — Differences of the Monthly Mean Barometric Pressures 

 at Greenwich and Dublin in thousandths of an inch. 



/32. 



Month. 



1 Q/l O 



1 O/f Q 



1844. 



1845. 



1846. 



1847. 



1848. 



1849. 







+ 97 



— o 



+ 114 



+160 



+ 163 



+ 36 



+ /9 



February . . . 





OA 



— bO 



+ 2 



+ 33 



+ 66 



+ 7 



+136 



1 T AO 

 + 102 





+ 97 



+ 95 



1 oo 

 + 22 



— b8 



+119 



+ 53 



4- 8 



+ 13 





- 56 



+121 



+ 74 



+ 3 



- 55 



- 5 



+ 32 



- 28 



May 



+ 89 



+ 12 



-110 



-102 



+ 38 



+119 



+ 44 



+ 26 



Jane 



+ 80 



+ 4 



+ 70 



+ 60 



+ 67 



+ 1 



+ 73 



- 15 



July 



+ 51 



+ 24 



+ 8 



+ 56 



+ 84 



+ 14 



+ n 



+ 61 





+ 38 



+ 70 



+ 19 



- 15 



- 5 



- 10 



+ 84 



+ 52 



September . . . 



- 27 



- 20 



- 13 



+ 53 



+ 18 



+ 26 



+ 26 



- 57 





- 41 



+ 21 



+ 81 



+ 96 



+ 89 



+ 88 



+ 27 



+ 80 



NoTember . . . 



+ 119 



+100 



+ 74 



+137 



+ 137 



+ 119 



+ 18 



+ 92 



December ... 



+166 



+ 139 



+ 40 



+ 35 



+ 52 



+240 



+290 



+ 60 





+ 60 



+ 48 



+ 22 



+ 34 



+ .64 



+ 68 



+ 71 



+ 39 



Although we may assume, when observations for a considerable period 

 of time are considered, that the isobars over the small space about the 

 three stations may be represented by parallel straight lines, yet this 

 assumption becomes less probable when the observations for single 

 months are employed ; since in these occasional cyclones may produce 

 considerable irregularities. I have thought it desirable, however, to 

 calculate the values of & for each month by equation (4), in order to ob- 

 tain some approximation to the probable errors of the directions deduced 

 from the whole eight years' observations. The values of 6 are given in 

 the following Table. 



Table IY. — Directions of the Isobars (0) for each Month, counted from 

 North through East, South, and West. 



Month. 



1842. 



1843. 



1844. 



1845. 



1846. 



1847. 



1848. 



1849. 







o 









o 



o 







27? 



276 



298 



236 



248 



186 ■ 



216 



275 





242 



55 



296 



270 



275 



293 



265 



270 





268 



180 



288 



348 



256 



228 



292 



292 





78 



236 



262 



129 



340 



302 



131 



336 





232 



134 



41 



14 



263 



218 



269 



126 





274 



286 



262 



265 



253 



296 



251 



304 





263 



287 



290 



254 



259 



286 



270 



273 





270 



250 



290 



287 



303 



303 



257 



272 





242 



320 



342 



262 



258 



289 



267 



75 





307 



290 



243 



261 



257 



233 



239 



224 





210 



263 



219 



245 



210 



259 



289 



258 





262 



257 



133 



289 



203 



196 



205 



269 





268 



266 



280 



278 



256 



255 



251 



266 



Variations of Yearly 3Ieans. — The yearly mean barometric pressure 

 does not seem to vary according to any law (see last line of Table I.). 

 The greatest pressure at all the stations occurred in 1842, and the next 



