20 GEOGRAPHIC TABLES AND FORMULAS. [bull. 234. 
E. To refer to any other than the tahnlar longitude: Add O'^.IO for 
each 15° east of the ninetieth meridian, and subtract 0"M6 for each 
15° west of the ninetieth meridian. 
A few examples will illustrate the use of table 1. 
• 1. Required the time of upper culmination of Polaris for a station in longitude 90° 
west, for March 3, 1904. 
h. m. 
Astron. time, U. C. of Polaris, 1904, March 1 2 46. 6 
Reduction for two days, 7'".9 (B) (subtract) 7. 9 
Local mean time U. C. of Polaris, 1904, March 3 2 38. 7 
The required time ma}^ also be obtained by using- the table in the 
opposite direction, i. e., by taking the time for March 15, and adding 
the reduction as folloAvs: 
h. m. 
Astron. time U. C. of Polaris, 1904, March 15 1 51.6 
Reduction for twelve days, add 47. 3 
Local mean time U. C. of Polaris, 1904, March 3 2 38. 9 
In this case the two results are practically identical. If the compu- 
tation is made both ways, the results will check each other. B haa 
been inserted to save the surveyor the little trouble of making the 
multiplications; thus, for the above example, in the table under B, 
opposite the third or seventeenth day of the month in the left hand 
column, will be found the correction 7"\9. 
Computing from a preceding date, for days between April 11 and 
15 of any year, the reduction in B will be greater than the tabulated 
time of culmination, in which case 23^' 56'". 1 will be added, to make 
the subtraction possible. 
2. Required, for a station in longitude 90° west, tlie time of U. C. of Polaris for 
April 14, 1906: 
h. m. 
Astron. time, XT. C. of Polaris, 1906, April 1 47. 1 
Add 23 56. 1 
Sum 24 43. 2 
Reduction to April 14, subtract 51. 2 
Local mean time U. C. of Polaris, April 14 23 52. 
Working from a following date, for days between 9th and 15th of 
April, the sum will exceed 23^ 56™. 1, and when this occurs subtract 
23'' 56"M from the sum, and the remainder will be the required time. 
3. Required, for a station in longitude 90° west, the time of U. C. of Polaris for 
April 10, 1904. 
h. m. 
Astron. time, U. C. of Polaris, 1904, April 15 23 45. 6 
- Reduction for five days, add _ 19. 7 
Sum 24 05. 3 
Subtract 23 56.1 
Local mean time, U. C. of Polaris, 1 904, April 10 09. 2 
For further application of table 1 see pp. 26 and 27. 
