(JO ASTRONOMICAL OBSERVATIONS 



radius two fcrews, one beyond the fpeculum, and one 

 between it and the nonius, for the purpole : they had 

 button heads, and their fhanks were as high as the top 

 of the index fpeculum. 



On the back of the o61ant there was a fcrew with a 

 button head ; the thread entered the center pin, and the 

 fhoulder preffed upon the plate which keeps that pin 

 in its place. 



The back fcrew and vice fcrews being flacked, the in- 

 dex fpeculum was brought parallel to the horizon glafs; 

 then the vice fcrews were turned to join the fpeculum 

 to the index, as before the alteration was made. 



To extend the power of the oftant occasionally, it 

 was nicely adjufled : then the index was carried to 90% 

 and there fcrewed to the limb. Next the back fcrew of 

 the center pin was forced, till by its preffure the fpecu- 

 lum was held faft : after that, the vice fcrews being 

 flacked, the index was carried back to o°, and there 

 fcrewed to the limb. Whilft it was in this pofition, the 

 vice fcrews were again turned, which fix.d the fpecu- 

 lum-piece to the index, and then the back fcrew being 

 (lacked, the fpeculum followed its motions. When it 

 was ufed, the index fhewed the angle which was to be 

 added to 90 for the angular diftance. 



By this contrivance, with an oftant, I could take 

 angles of 150 ; and confequently meridian altitudes 

 as far as 75 : and if the horizon glafs and telefcope 

 could have been made to Aide nearer towards the cen- 

 ter, it would have increafed (till further. 



In Ramsden's new quadrant there is a fcrew to adjuft 

 the horizon glafs, and bring it parallel to the other ; 

 provided the index fpeculum is perpendicular to the 

 limb, this is all well ; but if that be inclined, as foon as 

 the index quits o°, there will be an error in the angles 



obferved. 



