on the Slate of the Barometer. r^^ 



je6l ; and in particular, moft of the members of our meteoro- 

 logical focictv, among whom M. Steijilehner, Phmer, and 

 Chimincllo, have taken great pains. The lirll fays, that he 

 found, by feveral comparative obfervations, that the greateft 

 fall of tlie barometer docs not happen in very remote phices 

 at the fiime time, hut that it is earlier towards the wefl, and 

 later towards the eaft, and that the difference of the time is 

 nearly equal to the difference of the meridians of the places ; ati 

 aflcrlion wliich indeed del'ervestobe more accurately examined. 

 M. Planer obferved the barometer for a whole year, fix 

 times every d.iy, or every fourth hour of the natural day, at 

 two, fix, and ten in the morning, and at the fame hours 

 after noon ; and found, in general, that the barometer, be- 

 tween ten in the morning and two in the afternoon, and be- 

 tween ten at night and two in the morning, was lefs in its 

 rifing, and greater in its fall ; and that the contrary was the 

 cafe between the hours of fix and ten in the evening and 

 morning. M. Chimincllo obferved the barometer twenty- 

 two times a day for three )ears, but he left a chafm in the 

 night which he fupplied by calculation. The principal po- 

 fitions which he thence deduced, are, that the barometer 

 falls towards noon, as well as towards midnight *. 



'^ In examining a twelve-months' Rtgifter, kept by ■ Dunl>ar, Efq, 



rearthe banks of the Miffiilppi, in N. lat. 31" z8', and long. 91" 30' W. 

 of Greenwich, which, for the greater facility of comparilbn, I have laid 

 down, with others, on a fralc iu the manner I have heretofore exhibited, 

 tilers occurs a remarkable irftance of a diurnal variation. For the fpace 

 of about four days before, and fix days after the fummer folftice, the ba- 

 ronuter regularly rifes from about 9 P. M. to al out 6 .\. M. then falls till 

 the return of the forn^er hour in the evenina, then rifes again as before, 

 &c.in alternate periods. In the fiift four days the dirt6>ioii is Gfcmdhi^^ 

 and the elevation of a line drawn through the mean is about _*_ of aa 

 inch. In the latter fix days the mean line is perfeftly horizontal, the ele- 

 vation each night amounting to -j-^^ and the depreffion each day to the 

 fame, but occupying double time. 1 he thmes above given are thofe at 

 which the obftrvations \ve:e made, but it is probable that the maximum 

 and minimum each day correfponded rather with the times of fun-rife ar, J 

 fun-ftt. The firft peiiod of four days was dry, with 3 temperature of gi"* 

 in the middle of the day. This ended in a thunder ftorm, on the zifl; of 

 the month, with 0,82 inches of rain. The beimmcter, after this, rofc _♦_ 

 in the nii;ht, then retijaintd moltly flationary, with cloudy weather, until 

 the evening of the 26th, beginning a I'econd period of fix days, during 

 which brifk winds at S. S. E. and S. W. prevailed with rain every after- 

 noon or evening, amounting, iu all, to 1,7 inches. Temperature H^". 'Ihc 

 ■vvhole occupied juft the fpace between full and new moon; and there arc 

 traces of the operation of tliis periodical influence in other parts of the 

 Hcirifter. 



I fliall not prcfume, at prcfent, to nfcribe this vriri::tion enrirelv to jij.ine- 

 {.iry influence; but the fatis iii't woitliy examination tn that relpttr. L. H. 



.3 The 



