METHODS OF FINDING MERIDIAN ALTITUDE. 32& 



N. B. The number of seconds in table XVIII may be Method of 

 found independent of the tabic, thus; add the constant r idian°altitude 

 log. 0.29303, the log. cosine of latitude by account, and and approxi- 

 log. cosine of declination together; and subtract the log, two altitude.° m 

 sine of the difference or sum of the latit. and declin. ac- 

 cording as they are of the same or different names ; the 

 remainder will be the logarithm of the number of seconds 

 in table XVIII. 



If to this log. be added twice the log. of any number of 

 minutes less than 30 minutes, the sum will be the logarithm 

 of a number of seconds; which added to the altitude, taken 

 at that number of minutes from noon, will give the wie- 

 ridian altitude, the same as above. 



REMARKS. 

 1. If the number of seconds that the sun or moon's de- 

 clination changes in one minute, be divided by twice the 

 number of seconds found from table XVIII, the quotient 

 in minutes will be the Correction of Noon, from equal 

 altitudes, for any less interval of time than twenty 

 minutes. 



2. This correction is also tlie time, in minutes, between 

 the sun and moon's greatest altitude and meridian al- 

 titude. 



3. And if this correction be multiplied into half the num. ' 

 ber of seconds that the declination varies in one minute, 

 the product will be the difference, in seconds, between the 

 sun or moon's greatest and meridian altitude, which, re- 

 specting the moon, is sometimes considerable; therefore as 

 the altitude found by this problem H -f-A is strictly the 

 greatest, not the meridian altitude, and the time F and G 

 is the time before and after the greatest attitude: this pro- 

 duct should be applied as a correction to reduce the moon's 

 altitude when thus found, to her true meridian altitude, 

 when that is required. 



See also Remark 2 on the page next but one. 



fROBLEar 



