376 Portable Instrument for acquiring 



the top of a post, &c., lines may be drawn on the stand in the 

 direction of the sides A B, A C, or B C, by means of which it 

 may at any time be replaced with little trouble. ..„.,, |^ , 



Problem 2. The instrument being correctly ' pMfced and 

 levelled, the next operation will be to adjust the conical 

 projection to the day and hour of observation. 



Turn the cone round till the day of the month on the circle, 

 at the bottom of it, coincides with the hour and minute on the 

 circle E F G. 



Example. — To adjust the cone for the 15th January, at 

 twenty minutes past nine at night. Turn the cone till the 

 15th January on the circle attached to it coincides with IX h. 

 20 m. P. M. on the circle E F G. 



Problem 3. The cone being adjusted, and any star pro- 

 posed, to find its place in the heavens. 



The cone remaining at rest, turn the declination segment K 

 till the scale L cuts the proposed star on the projection ; note 

 its declination on the scale and set the index M to the same 

 degree on the segment K, when the index will point to the 

 star, which, if the adjustments have all been correctly made, 

 will be seen through the sights P, O. 



Example. — To find the star Aldebaran ; look for Aldebaran 

 on the projection, bring the scale L to cnt it, and you will find 

 it against 16° north declination. Set index M to 16° N. P., and 

 look along the edge of it, or through the holes P, O, and you 

 will see the star. 



Problem 4. Having observed a star in the heavens, to find 

 it on the projection. 



Set the cone as accurately as you can to the day and hour, 

 then turn the declination segment round, and elevate the index 

 till you can see the star through the sights P, O. Note the 

 declination at the segment K, cut by the index M, and against 

 the corresponding degree of the scale you will find the star on 

 the projection. 



If no such star can be found, you may then conclude that 

 it is a planet, or a new star. 



By this means the place of the moon, of a planet, or a 

 comet, may be noted down, from time to time, and their ap- 

 parent paths traced out. 



