■ 57 



hammering; upon annealing in a charcoal fire, the mean 

 density of five out of the ten pieces was 8*896, showing a gain 

 of 0*018 upon the hammered pieces, and a loss of 0*002 

 upon the original. A third series of experiments upon the 

 change of density in a bar of copper by successive hammerings 

 showed a loss of density from 8*885 to 8*867. 



The Author considered there was a connexion between these 

 phenomena and the heat disengaged in the hammering of the 

 copper; he conceived it possible that the expanded state of 

 the copper while heated by hammering was retained, and that 

 the efi'ect of annealing might be to allow the molecules or 

 particles to recover the state in which they were in before 

 being disturbed by the heat produced in hammering. 



PHYSICAL AND MATHEMATICAL SECTION. 

 February 28th, 1861. 



Mr. G. V. Vernon, F.R.A.S., read a Paper, " On the 

 Irregular Oscillations of the Barometer at Manchester." 



This Paper is an addition to one upon the same subject 

 brought before the Society by Mr. Baxendell, F.R.A.S. 



The tables appended to it give the total amount and 

 number of the barometer oscillations at eight a.m., for each 

 month from 1849 to 1860, inclusive ; the mean daily 

 amount ; the monthly fall of rain, and its difference from the 

 average of twelve years, and Dr. Dal ton's forty-seven years' 

 average. For the month of August, the Author was indebted 

 to the kindness of Mr. John Curtis, in supplying him with baro- 

 meter observations, which were deficient in his own register. 



The maximum amount of oscillation takes place in January, 

 and the minimum in July, to which may be added a second 

 maximum appearing to take place in October. The mean 

 total amount of oscillation for the year is 6 14 10 inches, and 



