26 RULES FOR FINDING THE EQUATION FOR THE 



No. IV. 



A short and easy rule for finding the equation for the change of the 

 swis declination when equal altitudes are used to regulate a clock 

 or other time keeper. Communicated by Andrew Ellicott Esq. 



Read January 16th, 1801. 

 FOR THE FIRST PART. 



FIND the Sun's longitude, declination, and the change 

 of declination for 24 h at the time of the observation, like- 

 wise find the proportional part of the change of declination 

 for the half interval between the forenoon and afternoon ob- 

 servations, then take the proportional logarithm answering to 

 the change of declination for the half interval, (increasing the 

 index by 10,) from which take the log. cosecant of the 

 horary angle; to the remainder add the log. cotangent of the 

 latitude of the place of observation, and take out the minute 

 and second from the P. Ls. answering to the sum (10 being 

 deducted from the index) which converted into time will give 

 the first part of the correction and will be deductive in North 

 latitudes, when the sun's longitude is 0, 1, 1, 9, 10, or 11, signs, 

 and additive in the others; but the contrary in South latitudes. 



FOR THE SECOND PART. 



TO the P. L. of the change of the sun's declination during 

 the half interval, add the log. cotangent of the sun's declination, 

 from that sum deduct the log. cotangent of the horay angle. — 

 Takeout the minute and second from P. Ls. answering to the re- 

 mainder, which turned into time will give the second part of 

 the correction ; this is common to all latitudes, and will be 

 additive when the sun's longitude is 0, 1, 2, 6, 7, or 8, signs s 

 and deductive in the others. 



