136 EXCURSIONS IN MADEIRA 



Cape Coast or Sierra Leone. I made the variation 22" 17' W. 

 I could only afford to furnish myself with Kater's pocket azimuth 

 compass for this observation, but I took the precaution to deter- 

 mine its error (2°) at the observatory. The azimuth circle at the 

 foot of my reflecting circle, having a nonius by which it may be 

 read within a minute, I preferred bringing down and determining 

 the distance of the sun from any remarkable object in the horizon 

 at each observation, and bearing that object leisurely afterwards, 

 to bearing the sun itself at each observation, having no assistant, 

 and the compass being graduated only to degrees. 



I had the reflecting circle made, to use occasionally on a foot, 

 like a repeating circle with a moveable level, to obviate the 

 inconvenience of being unable to take meridian, or indeed double 

 altitudes of the sun, with an instrument of reflection in those 

 parts of the interior of Africa approaching the equator, since in 

 using the artificial horizon, the sextant will not measure an 

 altitude exceeding 60°. It is rather hard upon a traveller to be 

 obliged to keep awake to watch the culmination of a star, after 

 being worn out by a hard day's march. Baron de Humboldt 

 proposes placing the index glass at an angle, say 30°, to the false 

 horizon glass '', which I have done to an old wooden sextant which 

 I keep in reserve ; but I do not see how it is to be rectified from 

 time to time in a close inland country, where the whole circle of 

 the horizon is rarely visible, unless by another instrument. 

 Mr. Beauchamps ' submits the plan of inclining a glass 45°, on the 

 artificial horizon, which would enable the observer to measure the 

 greatest possible attitude, but I confess I do not immediately see 

 how the angle of inchnation could be verified from time to time 

 with facility; and it must always be recollected that measuring 

 the meridian or correspondent altitude of a star by means of an 



'' Voyage Partie Astronomiqiie, 2 vol. 4to. vol. I. p. 9. 

 ' Memoires sur PEgt/pt, t. II. p. 109. 



