/. Description of an Improvement in the application of the Quadrant of Alti- 

 tude to a Celestial Globe, for the Resolution of Problems dependant on Azi~ 

 muth and Altitude. By Mr. John Smeaton, F.R.S. Anno 1789. Vol. 

 LXXIX. p. 1. 



The difficulty that has occurred in fixing a semi-circle, so as to have a centre 

 in the zenith and nadir points of the globe, at the same time that the meridian 

 is left at liberty to raise the pole to its desired elevation, Mr. S. supposes, has 

 induced the globe-makers to be contented with the strip of thin flexible brass, 

 called the quadrant of altitude ; and it is well known how imperfectly it performs 

 its office. The improvement he has attempted, is in the application of a qua- 

 drant of altitude, of a more solid construction ; which being affixed to a brass 

 socket of some length, and this ground and made to turn on an upright steel 

 spindle, fixed in the zenith, steadily directs the quadrant, or rather arc, of alti- 

 tude to its true azimuth, without being at liberty to deviate from a vertical 

 circle to the right hand or left : by which means the azimuth and altitude are 

 given with the same exactness as the measure of any other of the great circles. 

 With respect to the horary circle, as the common application seems very con- 

 venient on account of the ready adjustment of its index to answer the culmina- 

 tion of any of the heavenly bodies ; and as a circle of 4 inches diameter is 

 capable of an actual and very distinguishable division into 720 parts, answerable 

 to 1 minutes of time each, which may serve a globe of the largest size ; it seems 

 that it should rather be improved than omitted ; and if, instead of a pointer, an 

 index stroke is used in the same plane with that of the divisions, the single mi- 

 nutes, and even half minutes, may be readily distinguished. This globe, though 

 mounted merely as a model for experiment, and only 9 inches in diameter, ap- 

 pears capable of bringing out the solution to a quarter of a degree; which may 

 be esteemed sufficient, not only as a check on numerical computation, but to 

 come near enough to find stars in the day-time in the field of telescopes, which, 

 having no equatorial motion, are only capable of direction in altitude and 

 azimuth ; but from globes of a larger size, we may expect to come proportion- 

 ably nearer. 



Mr. S. adds a minute description of the several new parts of this globe, which 

 is illustrated with a large plate of the same; not necessary to be reprinted here. 



