394 FEUGUSON'S LECTURES. 



with the sun and clock ; and so brought to a very great 

 exactness. 



N. B. The rays transmitted through the hole, will 

 cast but a faint image of the sun, even on a white screen, 

 unless the room be so darkened that no sun-shine may 

 be allowed to enter, but what comes through the small 

 hole in the plate. And always, for some time before the 

 observation is made, the plummet ought to be immersed 

 in a jar of water, where it may hang freely ; by which 

 means the line will soon become steady, which other- 

 wise would be apt to continue swinging. 



As this meridian line will not only be sufficient for 

 regulating of clocks and watches to the true time by 

 equation tables, but also for most astronomical pur- 

 poses, I shall say nothing of the magnificent and expen- 

 sive meridian lines at Bologna and Rome, nor of the 

 better methods by which astronomers observe precisely 

 the transits of the heavenly bodies on the meridian. 



