250 Mr. Dalton on Meteorology. [Aprh, 



ber, November, and December, are all below the mean ; those 

 for November and December are nearly one-tenth of an inch 

 below the mean. 



These results were quite new to me. On looking over the 

 observ-ations in the fourth volume of the Memoirs, however, I 

 found that similar results had been obtained by Mr. Hutchinson, 

 from an average of 25 years' observations at Liverpool ; namely, 

 from 1768 to 1792 inclusive ; and this period being entirely ante- 

 rior to the one above, is of course totally independent of any 

 fortuitous events in that period. Mr. Hutchuison's results, 

 corrected for temperature, will stand as under ; namely, 



Jan. 29-75 ; Feb. 29-61 : March, 29-82 ; April, 29-79 ; May, 

 29-78 ; June, 29-79 ; July, 29-78 ; Aug. 29-77 ; Sept. 29-67 ; 

 Oct. 29-71 ; Nov. 29-67 ; Dec. 29-68 ; Mean, 29-73. 



Here the months INIarch, April, May, June, July, and August, 

 are all above the mean, and the remaining six months are all 

 below it, except January. 



Wishing to have further corroboration of the fact, I had 

 recourse to the register kept by order of the President and 

 Council of the Royal Society, and collected the whole series of 

 observations of the barometer for 38 years. I found the results, 

 corrected for temperature, as mider ; namely, 



Jan. 29-87; Feb. 29-86; March, 29-93; April, 29-85; Mayy 

 29-88; June, 29-93; July, 29-87; Aug, 29-91 ; Sept. 29-88; 

 Oct. 29-84 ; Nov. 29-82 ; Dec. 29-84 ; Mean, 29-87. 



Here again the months March, May, June, July, August, and 

 September, are all at or above the mean; and January, February, 

 April, October, November, and December, are all at or below 

 the mean.* 



By comparing all these together, it would seem to be esta- 

 blished as a fact, that from March to September, the weighit of 

 the atmosphere is greater than from September to March in this 

 part of the world. This cannot be ascribed to the account of 

 rain ; for the summer period contains wet months as well as dry ; 

 and in the London averages, the month of April is in the low 

 period, though the driest in the year. It cannot be ascribed to 

 temperature ; for the month of November is warmer than March ; 

 yet this last is in the high period by all the tables, and the 

 former in the low period. Notliing appears to me indicative of 

 the periods but the declination of the sun ; it seems that when 



• I cannot refrain from the remark that some of the annual tables of the Royal 

 Society's meteorolo^, exhibit marks of extreme carelessness. In the table for 

 1815, 1 found/o«r out nf the twelve monthly means of the barometer greatly erro- 

 neous: namely, January, Ajiril, ■May, and October. The monthly means for 

 August, 1807, and Septenibei, ls08, are also ^rfa//j/ wronj;. These errors were 

 detected by a comparis,)n with my results for the same months; as I found the 

 results at both places irreconcileable according to the known laws of barometry. 

 As tho above w ork, sanctioned by such authority, will naturally be regarded as a 

 national standard in meteorology, it is greatly to be desired that the whole of th« 

 fables were revised and corrected. 



