305 



to, namely, to take as dew-point, the mean of the temperatures 

 indicated by the inner thermometer at the instant of the de- 

 position of the dew, and at that of its disappearance, the 

 result is necessarily higher than the truth. 



Dr. Apjohn concluded, by drawing attention to the great 

 value of the other tables alluded to in Captain Boileau's 

 letter, the construction of which, must have been a work of 

 immense labour. Two of these greatly simplify the calcula- 

 tions necessary in applying the hygroraetric formula, as the 

 arithmetical operations are thereby reduced to mere addition 

 and subtraction. 



The third table gives the force of vapour to tenths of a 

 degree Fahrenheit, throughout the entire range included 

 between — 3° and + 146, Fahrenheit, calculated de novo by 

 the well known method of Biot, from the experiments of 

 Dalton and Ure. It does not materially differ, except in its 

 greater extent and minuteness, from the table of the tension of 

 aqueous vapour which Dr. Apjohn has hitherto used, and 

 the superior accuracy of which, as compared with the table 

 of Kaemtz, and that not long since published by the Meteor- 

 ological Committee of the Royal Society, has been rendered 

 highly probable by Professor Lloyd. 



Professor Mac Cullagh read a paper on the Catalogue of 

 Egyptian Kings, which is usually known by the name of the 

 Laterculum of Eratosthenes. 



This Catalogue, which the distinguished mathematician 

 and philosopher whose name it bears drew up by com- 

 mand of Ptolemy Euergetes, contains a long series of kings 

 who reigned at Thebes in Upper Egypt ; and has been pre- 

 served to us in the Chronographia of Georgius Syncellus, a 

 Greek monk of the eighth century. It is a document which 

 has been made much use of by chronologers ; by some of 

 whom, as by Sir John Marsham for example, who calls it 

 " venerandissimitm antiquitatis monumentum" it has been 

 reckoned of the very highest authority ; but it is extremely 



