of a . more complete Map of the Heavens. 177 



operation while looking into the telescope. The degree of 

 force used in clamping the screws will cause a slight alteration 

 in the position of the two images, which may be subsequently 

 remedied in a similar manner. 



That the telescope should have an equatorial motion, and be 

 provided with an apparatus for minute changes of the axis, is 

 clear from the preceding description. 



I shall now add some observations as originally noted down, 

 together with their comparison with meridian observations, 

 in order to give some idea of the degree of accuracy which may 

 be attained by single readings off. 



Position in 1800. Star compared. 



Name. 



8 Orionis 



5 h 2l m 4?Sj6 



-0° 27',5 



Above — ; Below + ; Right + ; Left — ; 1 Division = 2'-866. 



The telescope used is one by Fraunhofer, of 34 w aperture, 

 42" focal length, and magnifying 23 times : observations with 

 a sweeper would be somewhat more uncertain # . 



As the scale which has been adopted in the maps, does not' 

 well admit of greater accuracy than 0',5 in the position of the 

 stars, no sensible error can arise from this method of observing^ 

 even with a sweeper. By the former methods, errors amountr 



* [I do not understand the notation here introduced; but I presume 

 it means 34 Paris lines (= 3 English inches), and 42 Paris inches^ = 45 

 English inches) : at least, these are the dimensions of my telescope, — F. B.] 



New Series. Vol. 4. No.21. Sept 1828. 2 A 



ing 



