' 77 



contain more than 20 or 25 pages, A table also by which 

 the moon's parallax* may be taken out by inspection, will 

 greatly assist this as well as every other method, and for this 

 method it should be arranged in the manner of tables of 

 sines and cosines, so that the parallax answering to the com- 

 plement of the moon's altitude, may be found by the side of 

 the parallax itself. But the parallax for any altitude, and 

 for its complement, are so readily found by help of the very 

 valuable table of proportional logarithms in the requisite 

 tables, that the want of the abovementioned table can 

 scarcely be offered as an objection to the practice of this 

 method : particularly when it is considered that the use of 

 proportional logarithms must be familiar to all who use the 

 lunar method, being necessary in a subsequent part of the 

 operation. 



The product (a+(3+y+£) (v. sin D — ^v, sin A) will easily be 

 had by a table of logarithms to five places, and indeed to 

 those to whom contracted decimal multiplication is familiar, 

 it will be scarcely worth while to have recourse to a table of 

 logarithms. The odd seconds in D should be reserved, and 

 as H & H' should be only put down to the nearest minute, 

 seconds will only be used for v. sin a and v. sin d. 



6. Mr. Dunthorne's table for the value of log N (the 9th 

 of the requisite tables) is of considerable extent, and requires, 

 that it may be used with convenience, to be even farther 



VOL. XI. M extended 



* For low altitudes it seems absolutely necessary to use separate tables for parallax 

 and refraction, instead of a table for the correction of the moon's altitude, on account of 

 the variations of the refraction ascertained by the changes in the barometer and therrao- 

 neter. Refraction is sometimes changed by ^ of its mean quantity. 



