5230 On the time at which Nearehua left the Indus. 



be accounted for by the constant care and attention which 

 were applied by the ancients to these observations. At one 

 time, indeed, the whole of astronomy comprised hardly any 

 thing else ; and they certainly possessed many advantages, 

 when more accurate means of information were unknown, for 

 the common purposes of human life. Since modern science 

 has directed us to better ways of observation, these have of 

 course become neglected, and disuse lias thrown a degree of 

 obscurity over them, when, in truth, there is nothing really 

 intricate in their nature. When a star rose exactly at the 

 same time in the morning with the sun, or set exactly at the 

 same time with it in the evening, it was said to rise or set cos- 

 mically : and when a star rose exactly at the same time in the 

 evening at which the sun set, or set in the morning exactly at 

 sunrise, it was said to rise or set acronychally. 



These were the four fundamental combinations, by the re- 

 turns of which the ancients marked their seasons; but, as the 

 stars cannot be visible when the sun is on the horizon, they 

 could never be the objects of immediate observations. It 

 became necessary, therefore, both for approximation to the 

 true synchronisms and for estimates of the lapse of time, to 

 observe the stars as long as they were visible before sunrise, 

 and as soon as they became visible after sunset ; and it is clear, 

 from this general view, that whether we consider them cosmi- 

 cally or acronychally, the visible risings must always be later 

 than the true, and, on the contrary, that the visible settings 

 must take place sooner than the true. 



When the star emerged from the sun's light, so as to be 

 first distinguished before day-break in the east, it was said to 

 rise heliacally ; and when it sunk into the sun's light, so as to 

 cease to be visible in the west after sunset, it was said to set 

 heliacally. These phenomena are so repeatedly alluded to, 

 that, if Strabo's date had been the morning instead of the 

 evening rising of the Pleiades, it is impossible that t)r Horsley 

 could have had any difficulty. But we have here a very re- 

 markable instance of the use and influence of names. The 

 ancients did not confine themselves to the strict acronychal 

 risings and settings ; they likewise attended particularly to the 

 last visible rising of a star in the evening, and its first visible 



