Problems of Nautical Astronomy. 121 
stars altitude, N ; observing that the same table will do for the 
moon and star ; but a fourth table should be made for the sun, 
so as to include its parallax; and, lastly, let a fifth table be made, 
with the moon's altitude for argument, giving the logarithm of 
— , which call C. Then will cos. G — S- Sap C— — — ^ 
a na’ r a o 
+ bp-\- D— A. 
“ It must be observed that Sap C=Sp e — whereas it ought 
to equal Sp g — <5^; but ^ cannot exceed 57", and the horizontal 
parallax cannot differ from the mean by more than T r y part of 
the whole; so that the error arising from thence cart not exceed 
3" or 4". This small error however may be diminished by 
giving the quantity C for more than one horizontal parallax." 
Addition to the foregoing Letter. 
“ I have procured tables of the above-mentioned kind to be 
computed, which are intended to be inserted in a work now 
printing by Mr. Mendoza y Rios. Allowance is made in them 
for the alteration of the refractive power of the atmosphere, 
v/hich is done by two new tables, one giving the correction of 
the logarithms M and N, and the other the sum of the correc- 
tions of dp and Sv. Now it must be observed, that the quantities 
p. and v vary only from 57" to 51"; and therefore the correc- 
tions of Sp and Sv, may, without any material error, be consi- 
dered as the same at all altitudes ; and therefore the sum of the 
corrections may be comprehended in a table, under a double 
argument, namely, the refractive power of the atmosphere and 
the apparent distance. 
MDCCXCVII. 
R 
