NEW ASTRONOMICAL INSTRUMENT. 



m the heavens. The outermost of these is divided into I5«sc"ption of 



an astrometer 

 360 equal parts, and the other, which is a scale of am- fo, determining 



plitudes, is so formed, that the amplitude of any of the g^^^^^^f/jfj ^f' 

 heavenly bodies mav be exactly opposite the corresponding the stars, &c„ 

 degree of declination in the adjacent circle. The degrees 

 of south declination, for instance, in the latitude of 51**, 

 'Corresponds with an amplitude of 15f°, consequently the 

 fifteen degrees of amplitude must be nearly opposite to the 

 tenth degree of declination ; so that by a table of ampli- 

 tudes, the other points of the scale may be easily deter- 

 mined. The astrometer is also furnished with a moveable 

 index M N, which carries at its extremities two vertical 

 sights WW, in a strait line with the center A. The instru- 

 ment being thus completed, let it be required to find the 

 planet Saturn, when his declination is 15® north, and the 

 time of his southing 3^ 30' in the morning. The times ol 

 his rising and setting will be found to be 7^ 15', and 10** 45', 

 and liis amplitude 24® north. Then shift the moveable 

 index till the side of it which points to the center is exa.ctly 

 above the 24th degree of the exterior circle in the north- 

 cast quadrant, and when the line A B is placed in the me» 

 ridian, the two sight holes will be directed to the point of 

 ithe horizon where Saturn will be seen at 7^ 15', the tinje of 

 liis rising. The same being done in the north-west qua- 

 drant, the point of the horizon where the planet sets will 

 likcAvise be determined. In the same way the position of 

 the fixed stars, and the other planets, may be easily dis. 

 covered. 



If it is required to find the name of any particular star 

 that is observed in the heavens, place the astrometer due 

 north and south, and when the star is near the horizon, 

 cither at Its rising or setting, shift the moveable index till 

 the two sights point to the star. The side of the index will 

 then point out, on the exterior circle, the stars amplitude. 

 With this amplitude enter the third scale from the centre, 

 and find the declination of the star in the second circle. 

 Shift the moveable horary circle till the time at which the 

 observation is made be opposite the star's declination, and 

 the index B will point to the time at which it passes the 

 Meridiane The difference between the time of the star's 

 ^ C 2 southing. 



