IS! 3.] Barometer in London, Paris, and Geneva. 409 



Geneva on the 7th. In November the barometer stood lowest 

 in London on the 3d, in Paris and Geneva on the 4th. As 

 these alterations in the weight of the atmosphere begin usually 

 at London, they seem to proceed chiefly in a direction from west 

 to east ; but this commencement in London is not without ex- 

 ception. In May, 1807, the barometer was lowest at Paris on 

 the 29th, at London and Geneva on the 30th. 



Though the curves have a great resemblance to one another 

 upon the whole, yet there are some particulars in which they 

 differ: for example, in London the barometer sunk without 

 interruption from the 13th to the 21st of January, 1807; while 

 in Paris and Geneva it made several oscillations during the same 

 time, which agree with each other in these two cities. On the 

 13th of January, 1807, the barometer sank slowly in Paris and 

 Geneva ; but in London it descended with such velocity that in 

 48 hours it had sunk 0"7I inch. The cause of this change in 

 the barometer must be very powerful, yet completely local, and of 

 very short duration, since the rate of the barometer agrees within 

 a day in London, Paris, and Geneva. It were to be wished that 

 we knew the state of the atmosphere at London on the day of 

 this rapid descent of the barometer. This knowledge would 

 probably throw some light on so sudden a fall.* 



I consider the present attempt to be sufficient to show how 

 important it would be to keep daily tables of meteorological 

 observations on different parts of the meridian and parallel of 

 Paris, and to exhibit these observations every year in the state of 

 curves. By this method more knowledge of the modifications 

 which take place in the atmosphere would be gained by a single 

 glance of the eye than by a painful comparison of voluminous 

 observations. To save trouble, tables might be published so 

 contrived that the observer would have no more to do than to 

 denote the daily observation by a point upon the table. At the 

 end of every half year the curve may be directly drawn. A copy 

 of such a graphic delineation might be sent to the central board, 

 which already exists under the name of Board of Longitude, and 

 holds its meetings at the observatory of Paris. Here a complete 

 table of all the observations would be constructed, and a copy of 

 it sent to every observer; from which he would see the fruit of 

 his labour, and be induced to continue his observations. The 

 choice of the places of observation, accurate directions for the 

 benefit of the observers, the precision of the instruments, and 



• In Great Britain it holds, without exception, as far as my observations 



thai when the barometer falls suddenly a violent >\ind soon follows, 



pql alweyg at the very place of the fall, but within BO very sri.n distance. I 



have do doubt that the fall alluded to by M. Pictet was followed by a violent 



eouth - v. ■• t-i.— T, 



