29 



elted. As a correct horary rate must be investigated, it may 

 save some trouble, to omit raising this rate to the quantity of 

 AR. corresponding to 12S and use the liorary rate obtained as 

 a member of the final analogy for the longitude. In this 

 case, the tables of logistic logarithms will supersede the use 

 of the table of assistant logarithms given in my first paper on 

 this subject.* It is also proper to observe, that a mode of 

 correcting the observed difference of the differences of the 

 AR. of the moon and star under different meridians, has been 

 suggested to me, by my learned friend, the professor of as- 

 tronomy in Trinity College, Dublin, which is suflficiently ac- 

 curate and universal ; it is, in fact, only a different mode of 

 effecting the purpose of my table 1. in the above-mentioned 

 paper, and either method may be applied. Previous to sub- 

 mitting to the Academy the results of my numerous compa- 

 risons of the observed differences of AR. of the j . the stars, 

 and the sun, for to obtain the difference of longitude of the 



observatories 



*It will be observed, that Mr. Brinlsley applies his correction of the observed 

 difference to the longitude immediately deduced from the entire observed diffe- 

 rence, by substracting from the longitude thus obtained, the whole observed 

 difference of the differences in sydereal time, of which he says, " this method 

 " of correction is universal, and may be explained thus:— 



" In the time the moon increases her AR. by the observed difference (D) of 

 the differences of AR. of 5 and * each meridian describes an angle in time 

 A = equdl to the angular distance of the meridians (L) + D. But, as horary 

 increase of AR. : D. :: i"" : A' and A' being reduced to *sydereal time, gives 

 A : and L = A — D or if L be taken =: to A^ — D reduced to sydereal time, 

 it will be sufficiently accurate." 



* For the horary increase being calculated to one hour of sular iimej the result will come out, a portioa 

 aolar time also, and therefore to be reduced to sydereal time. 



