281 



which would make the eclipse of Agathocles nearly central over the 

 northern station, and excludes the possibility of his passing by the 

 southern route. 



The author then adverts to the princijDal remaining causes of un- 

 certainty in these conclusions, and points out the values of progress- 

 ive change in the secular mean motions as peculiarly deserving 

 investigation. 



AUusion is then made to a record in the Persian poetical history, 

 preserved by Sir John Malcolm, which appears to point to a total 

 eclipse as occurring under similar circumstances in the province of 

 Mazenderan. It appears however on calculation, that no total 

 eclipse passed over Mazenderan, at least for many years, about the 

 time in question. 



The author then calls attention to the statement of Herodotus, 

 that something like a total solar eclipse occurred when Xerxes was 

 setting out from Sardes for his invasion of Greece. On calculation 

 it appears impossible to explain this by a solar eclipse, and moreover 

 the peculiar turn of the answer of the j\Iagi to the inquiries of Xerxes 

 would seem to be irreconcileable with a solar eclipse. The author 

 thinks it most likely that the phenomenon really was the total eclipse 

 of the moon which occurred on the morning of e.g. 479, March 14. 

 If this were adopted, the date of the invasion of Greece must be 

 brought down one year later than that given by the received chro- 

 nology. 



February 10, 1853. 

 LORD WROTTESLEY, V.P., in the Chair. 

 The following papers were read : — 



1. " On the determination of the Mean Temperature of every 

 day in the year, as deduced from the Observations taken at the 

 Royal Observatory, Greenwich, in the Years from 1814 to 1851." 

 By James Giaisher, Esq., F.R.S. Received Dec. 30, 1852. 



This paper has for its object the determination of the true distri- 

 bution of heat over the year, and is based upon an extensive series 

 of observations taken at the Royal Observatory during thirty- eight 

 years. 



In order to obtain a correct determination of the mean daily tem- 

 perature of each month, necessary to the proposed object, the author 

 at the commencement of his memoir explains how the entire series 

 of observations has been divided into groups, according to the re- 

 corded times of observation, for the purpose of applying the neces- 

 sary corrections calculated from his tables of Diurnal Range, published 

 in the Phil. Trans, for 1848. Having carefully explained his method 

 of arranging and testing his data, and providing for exceptional days, 

 upon which but few observations were recorded, the author gives 

 the results in twelve separate tables, which exhibit the mean daily 

 temperatures of every month in each of the thirty-eight years. In a 



