CONVERSION OF MEASURES OF TIME AND ANGLE. 



liii 



TABLE 76. Decimals of a day into hours, Tninutes aiid seconds. 

 Example : 



Convert o*?225 271 to hours, minutes and seconds : 



0.22 day = 4^^ 48™ + 28™ 48^ = 5^ \(i^ 48^ 



TABLE 76 



0.0052 day — 7™ 12^ + I7f28 = 

 0.000071 day = 6fo5 + 0.09 = 



29.28 

 6.14 



51* 24°^ 23S4 



TABLE 77. 



Minutes and seco?ids into decimals of an hour. 



The tabular values are given to six decimals. 

 Example : 



Convert 34™ 28'!7 to decimals of an hour. 



34m = 0^566667 



28^ = 7778 



o!7 = 194 



TABLE 77. 



TABLE 78. 



0.574639 

 Mean time at apparent noon. 



TABLE 70 



This table gives the time that should be shown by a clock when the 

 sun crosses the meridian, on the ist, 8th, i6th, and 24th days of each 

 month. The table is useful in correcting a clock by means of a sun-dial 

 or noon -mark. 



Example : 



To find the correct mean time when the sun crosses the meridian on 



December 15, 1891. 

 The table gives for December 16, ii*' 56°^. By interpolating, it is seen 



that the change to December 15 would be less than one-half minute ; 



the correct clock time is therefore 4 minutes before 12 o'clock noon. 



Table 79. 



TABLE 80. 



Sidereal time into mean solar time. 

 Mean solar time into sidereal time. 



TABLES 79, 80. 



According to Bessel, the length of the tropical year is 365.24222 mean 

 solar days,* whence 



365.24222 solar days = 366.24222 sidereal days. 



Any interval of mean time may therefore be changed into sidereal 



time by increasing it by its — : part, and any interval of sidereal time 



365.24222 ^ ^ 



may be changed into mean time by diminishing it by its 



366.24222 



part. 



*The length of the tropical year is not absolutely constant. The value here given 

 is for the year 1800. Its decrease in 100 years is about 0.6 s. 



