[ 2^1 ] 



I 



during the interval of the obfervations. As the greateft varia- 

 tion of the moon's femidiameter is about i6' in a day, in 

 this extreme cafe, under meridians that are 6H. afunder, the cor- 

 redtion of the difli from this caufe only would amount to 4". 

 And fhould (he in the interval have changed her declination, fo 

 as to vary her femidiameter by another fecond in the fame di- 

 redion with the former variation, then the aggregate of thefe 

 alterations of the lunar dillc would colledively amount to five 

 feconds, a quantity that would make a confiderable error in 

 the determination of the longitude. 



The neceffary corredions being found from the eftimate lon- 

 gitude and the tables, and carefully applied, all that remains 

 to be done is to ftate over again the analogy mentioned in the 

 general rnle, fubftituting therein the correded numbers. To ren- 

 der this final analogy as brief and as eafy as poffible, I have 

 added a fecond table of affijlant logarithms for every minute 

 of the moon's increafe of A. R. for 12H. in v/hich the arith- 

 metical complement of the proportional logarithm of the quan- 

 tity of the moon's increafe of A. R. in 12H. for every change 

 of i' in her rate is added to the proportional logarithm of 12H. 

 fo that all that is neceffary is to change the correded differ- 

 ence in time into parts of a degree, and to add its proportional 

 logarithm to the logarithm taken out of the table, and the fum 

 will he the proportional logarithm of the difference of the two 

 meridians in time. 



Dd 2 



EXAMPLE. 



