18 INSTRUCTIONS FOR MAKING FOREST SURVEYS, ETC. 



MIZAR 



If a survey is to be made in a region which has not 

 been subdivided by Government land surveys or where 

 the variation of the needle is not known, then the sur- 

 veyor must do one of three things. 

 He should if possible find the 

 variation by observing the Pole 

 Star, of which approximate bear- 

 ings are given (Table 1) at 9 p. m. 

 during the year ; or he may obtain 

 the true meridian by observing the 

 sun at apparent noon. If neither 

 can be done, a variation may be 

 assumed after examination of 

 figure 3, and this assumed varia- 

 tion should be entered in the field 

 notes and shown on the map, with 

 the date when the map is pre- 

 pared. 



POLARIS I - N - POLE 



OBSERVING POLARIS. 



. 



T: / 



The Pole Star is not exactly 

 above the North Pole of the 

 earth, but its bearing is due north 

 twice a day, and an observation 

 of it at one of these times will 

 give a true meridian. Mizar, a 

 double star in the bend of the 

 handle of the Big Dipper is either above or below the 

 Pole Star at these times. The same is true of the star 

 d (Delta) in the constellation Cassiopeia. (See fig. 4.) 

 At all other hours the Pole Star has a bearing either 



FIG. 4. Position of the Big 

 Dipper and Cassiopeia when 

 Polaris is due north. If the 

 figure is held upside down it 

 shows the reverse position in 

 which Polaris is also due 

 north. 



