The difference between mean noon, when the sun should be on the 

 meridian, and apparent noon when the sun actually is on the 

 meridian, is called the ''Equation of Time." The tabular cor- 

 rections will be found in the Ephemeris Tables. 



Thus, in early November the sun has passed the meridian 

 more than 16 min. before mean noon. It is always well to begin 

 latitude observations some 20 min. before local noon, although 

 there will be seasons of the year when the sun will not attain its 

 greatest altitude until after local noon. 



Standard Time * will also qualify the argument, but this 

 should be studied out by reference to the map inserted between 

 pp. 163 and 164. In Western Texas, for instance, observations need 

 not begin until nearly 1 o'clock standard time; whereas in Erie, Pa., 

 they should begin shortly after 11. 



Procedure 



Follow up the lower limb of the sun, and when the maximum 

 altitude is found add the sun's semi-diameter, as 

 taken from the Ephemeris Tables, to the reading 

 on the vertical circle; subtract correction for 

 atmospheric refraction, as figured by interpolation 

 from the table, p. XXI, and correct this result by 

 the sun's declination: adding if south and sub- 

 tracting if north. The final result is the co- 

 latitude or the polar distance. 



To Obtain Latitude with the Solar Attachment 



A mechanical correction for the declination can be made as 

 directed above if the observation is made with the solar attachment. 

 Proceed as follows: 



Level the instrument carefully, point the main telescope toward 

 the south if in the northern hemisphere and bring the solar telescope 

 into the same vertical plane by sighting both telescopes at some 

 distant point. 



If the sun's declination is south, elevate the telescope in the 

 northern hemisphere or depress it in the southern hemisphere. If 

 the sun's declination is north, reverse the order. With the main 



Adopted by the railr.xi nada, Kav. IS, ISM. 



