42 LIGHT SCIENCE FOR LEISURE HOURS. 



modern travellers and historians. One remarkable 

 instance of this may be cited. Mr. Layard has iden- 

 tified the site of Larissa with the modern Nimroud. 

 Now, Xenophon relates that when Larissa was besieged 

 by the Persians, an eclipse of the sun took place, so 

 remarkable in its effects (and therefore undoubtedly 

 total), that the Median defenders of the town threw 

 down their arms, and the city was accordingly cap- 

 tured. And Hansen has shown that a certain estimate 

 of the moon's motion makes the eclipse which occurred 

 on August 15, 310 B.C., not only total, but central at 

 Nimroud. Some other remarkable eclipses as the 

 celebrated sunset eclipse (total) at Borne, 399 B.C.; 

 the eclipse which enveloped the fleet of Agathocles as he 

 escaped from Syracuse ; the famous eclipse of Thales, 

 which interrupted a battle between the Medes and 

 Lydians ; and even the partial eclipse which (possibly) 

 caused the going back of the shadow upon the dial of 

 Ahaz 5 have all been accounted for satisfactorily by 

 Hansen's estimate of the moon's motion : so also have 

 nineteen lunar eclipses recorded in the Almagest. 



This estimate of Hansen's, which accounts so satis- 

 factorily for solar and lunar eclipses, makes the moon's 

 rate of motion increase more than twice as fast as it 

 should do according to the calculations of Adams. 

 But before our readers run away with the notion that 

 astronomers have here gone quite astray, it will be 

 well to present, in a simple manner, the extreme 

 minuteness of the discrepancy about which all the coil 

 has been made. 



