MONTHLY BAROMETRIC READINGS AT OLD TRAFFORD. 241 



responding methyl-compound, employing iodide of ethyl in 

 place of iodide of methyl. The two substances have pro- 

 perties so similar that it is almost impossible to distinguish 

 one from the other. 



XXX. Mean Monthly Barometric Readings at Old Tr af- 

 ford, Manchester, from 1849-72. By G. V. Ver- 

 non, F.R.A.S., F.M.S. 



Read before the Physical and Mathematical Section, October 14th, 1873. 



Having a tolerably complete register of barometric read- 

 ings, and knowing of no published normal values for any 

 station in or near Manchester, I have reduced and tabu- 

 lated the monthly means for the period above named. 



The barometer with which the observations were made 

 was a standard, by Negretti & Zambra, No. 266, and had 

 been compared at Greenwich. 



All the observations have been corrected for capillarity 

 and index-error to reduce them to the Greenwich standard, 

 and then reduced to 32 F. 



In the earlier part of the series I have unfortunately 

 some months deficient ; but in the latter part of the series 

 I have been able to fill up the gaps by the use of the very 

 careful series of observations made at Eccles by my friend 

 Thomas Mackereth, Esq., F.R.A.S., by applying correc- 

 tions determined by comparing the months in which the 

 observations were simultaneous. 



I found that the two series of observations were nearly 

 identical, after allowing for difference of level. 



The mean annual pressure for the entire series was 

 SER. III. vol. v. R 



