a Knowledge of the Stars. 373 



are, celestial globes, planispheres, and atlases, but none of 

 these afford such ready and certain means of finding or iden- 

 tifying particular fixed stars, as at first might be expected from 

 them. 



The Globe possesses the great advantage of being easily rec- 

 tified to the place of observation and adjusted to the exact 

 hour of the night. It likewise exhibits all the stars in their 

 proper situations of altitude and azimuth ; — but the constella- 

 tions being delineated on a convex surface, and viewed from 

 without, whilst the heavens appear to us a concave viewed 

 from within, the groups of stars are seen reversed, a circum- 

 stance which occasions no small degree of perplexity to a 

 learner. 



Planispheres and atlases exhibit the constellations as they 

 appear to the eye when on the meridian, but in a position very 

 different from that which they assume when removed far from it. 

 In short, except the pleiades and a few remarkable groups, it 

 is difficult to recognise a constellation in every position, without 

 great practice and continued observation. 



The Equatorial furnishes the best and readiest means of dis- 

 covering or identifying any particular star, but the great price 

 of this instrument, and the complicated nature of its adjust- 

 ments, render it unfit for learners. 



The instrument which we are about to describe, is in its 

 principle the same as the Equatorial, though not pretending to 

 any thing like the same degree of accuracy ; but it has this 

 advantage over it, — its adjustments are more simple and ob- 

 vious, consequently, better adapted to the capacity of learners ; 

 and it can be afforded at a very moderate expense, the price 

 not exceeding that of a common globe. 



A, B, C, D, is the stand of the instrument, composed of 

 three triangular pieces of wood glewed together, so that the 

 plane of the upper piece, D B C, makes with that of the lower 

 piece, A B C, an angle equal to the co-latitude of the place 

 it is intended for. 



On the upper piece, D B C, is described a circle, E F G, the 

 circumference of which is divided into twenty-four hours, and 

 every hour into twelve parts, equal to five minutes each. 



From the centre of this circle, and perpendicular to the 



