743 



March 4, 1848. 



The MARQUIS OF NORTHAMPTON, President, in the Chair. 



" On the Corrections necessary to be applied to Meteorological 

 Observations made at particular periods, in order to deduce from 

 them Monthly Means." By James Glaisher, Esq., of the Royal 

 Observatory. Communicated by G. B. Airy, Esq., F.R.S., &c.. 

 Astronomer Royal. 



The author, under whose immediate superintendence the whole of 

 the magnetical and meteorological observations taken at the Royal 

 Observatory at Greenwich have been conducted, by direction of 

 the Astronomer-Royal, has communicated in the present paper 

 various tabular results deduced from the meteorological observations, 

 reserving for future notice those deduced from the magnetical series. 

 His chief object has been to determine the corrections which are 

 applicable to the results obtained by different observers at various 

 times, so as to render them comparable with one another. The 

 barometrical and thermometrical observations here recorded have 

 been made at every hour of Gottingen mean solar time, during the 

 whole of five years, namel)^ from the end of 1840 to that of 1845. 

 The mean of each hour represents the results deduced from about 

 150 observations; those for each month represent about 1800 ob- 

 servations ; and those for the year represent upwards of 21,000 ob- 

 servations of each element. 



Tables are given representing the excess of the mean value of each 

 element at every hour of observation, in every month, above the mean 

 value for the month ; and also the mean of the numbers so found, 

 arranged for the different years, and likewise for the same hours in 

 every month. The numbers were then laid down on paper, as ordi- 

 nates to a curve of which the times were the abscissae, and a curve 

 passed through, or very near each point ; and the ordinates at every 

 Greenwich hour were measured from that curve, and their values 

 given in a table. The accordance of the results thus obtained for 

 the same hours in the same months of the different years is very 

 close and satisfactory ; and shows that observers may obtain very 

 valuable approximate results, by taking a comparatively small num- 

 ber of observations in each day at hours by no means inconvenient 

 in ordinary life, furnishing a close approximation to the mean and 

 extreme values, as well as to the diurnal and annual variations of 

 atmos])herical phenomena. 



March 9 and 16, 1848. 



The MARQUIS OF NORTHAMPTON, President, in the Chair. 



" Report of Experiments made on the Tides in the Irish Sea ; on 

 the similarity of the Tidal phenomena of the Irish and English Chan- 

 nels ; and on the importance of extending the experiments round the 



