6$ ASTRONOMICAL OBSERVATIONS. 



a mean of the eight good observations on the eclipses of the 

 1st satellite of Jupiter be taken, the longitude will be 5 h 5' 7". 3 

 which exceeds the longitude as taken from our maps but 1".3 

 and that of a mean of the whole collectively but 6". 7. From 

 which it appears, that the longitude may be considered to lie 

 between 5 h 5' 0."6, and 5 h 5' 7". 3 west from Greenwich, 

 without the possibility of a material error : I shall therefore for 

 the present call it 5" 5' 4". 



Observation on the going of the Clock. - 



The pendulum-rod of the clock is made of wood, as being 

 the most convenient for transportation, and not so liable to ac- 

 cidents as the gridiron-rod in removing the clock from one 

 place to another, in which way it has heretofore generally 

 been used. 



It was formerly supposed that wood neither expanded, nor 

 contracted, in the direction of the grain, with heat and cold ; 

 but this is not strictly true, though the alteration appears much 

 less than from wet and dry. When the atmosphere continues 

 for some time equally saturated with moisture, the clock has 

 always been found to go very regularly, notwithstanding the 

 great and sudden changes we experience in the United States, 

 from hot to cold, and from cold to hot. But the atmosphere 

 being charged at different times, with different degrees of mois- 

 ture, has a considerable effect, provided those changes from wet 

 to dry, and the contrary, are of sufficient duration : for it re- 

 quires several days' continuance of a damp, or dry atmosphere, 

 to produce any sensible effect. I have observed for several 

 seasons, that when the weather became warm in the spring, 

 the motion of the clock was accelerated; the contrary would 

 have been the case, had the pendulum-rod consisted of one 

 single bar of metal, because it would have expanded or 

 lengthened, as the weather became warm; but from the mo- 

 tion of the clock being accelerated, it is evident that the pen- 

 dulum-rod must have contracted, and this was probably oc- 

 casioned by the dry atmosphere, and drying winds, so preva- 

 lent at that season of the year, in this country. 



