420 The Rev. H. Lloyd on the Meteorology of Ireland. 



The best pair of homonymous hours, for the determination of the mean 

 temperature, and nearly also for that of the mean humidity, are O*" 46" A. m., and 

 9* 46" p. M.* Limiting themselves to the exact hours, the Committee might 

 accordingly have chosen either 9 a. m. and 9 p. m., or 10 A. m. and 10 p. m. ; 

 the former pair "was adopted, its superior convenience seeming to outweigh the 

 advantage of the latter in accuracy. 



For the fuller elucidation of some of the questions proposed, it was further 

 arranged that hourly observations should be taken at all the stations for twenty- 

 four hours, at the equinoxes and solstices, according to the plan laid down by 

 Sir John Heeschel. It was likewise provided, that hourly observations should 

 be taken occasionally, under special circumstances, such as storms, unusual dis- 

 turbances of barometric equilibrium, &c. 



For further details of the plan of observation, the reader is referred to the 

 " Instructions" prepared by the Council of the Academy. I now proceed to 

 the results of the observations. 



Tempeeature of the Air. 



Corrections. — It has been already stated, that the thermometers employed in 

 measuring the temperature and humidity of the air were carefully compared with 

 a standard thermometer, and their errors noted. When the errors differed by 

 more than 0°"2 in different parts of the scale, the instrument was rejected ; when 

 they did not, the mean of the observed errors was adopted as a constant error 

 for the whole scale of the instrument. Table ii. gives the numbers thus obtained 

 for the several instruments ; these numbers are applied, with the contrary signs, 

 as corrections to the observed results. 



It has been stated that the mean of the temperatures observed at 9 A. m 

 and 9 p. m. is, very nearly, the mean of the entire day. The small corrections 

 required, in order to reduce the former to the latter, are obtained from the 

 bi-hourly observations made at Dublin in the years 1840-1843. Table iii. con- 

 tains the results of that series, giving the mean differences between the tem- 

 perature at each hour of observation, and that of the entire day. 



* See the paper already referred to. The hours 9' 30" &. M., and 9'' SO"" P. a., are better for 

 humidity. 



