104 POPULAR LECTURES AND ADDRESSES. 



" the same distance. They are arranged from 

 " west to east, commencing- each day with the 

 " object which is at the greatest distance west- 

 " ward of the moon, in the precise order in 

 " which they appear in the heavens ; W. indicating 

 " that the object is west, and E. east of the moon. 



" The columns headed * P. L. of cliff.' contain 

 " the proportional logarithms of the differences 

 " of the distances at intervals of three hours, 

 " which are used in rinding the Greenwich time, 

 " corresponding to a given distance, according to 

 " the following rule, viz. : For the given day, 

 " seek in the Ephemeris for the nearest distance 

 "preceding, in order of time, the given distance, 

 " and take the difference between it and the 

 " given distance ; from the proportional logarithm 

 " of this difference, subtract the proportional 

 " logarithm in the Ephemeris ; the remainder will 

 " be the proportional logarithm of a portion of 

 " time to be added to the hour answering to the 

 " nearest preceding distance, to obtain the ap- 

 " proximate Greenwich mean time corresponding 

 " to the given distance. 



