and of the Altitude and Azimuth Instrument. 9 



numerous ; they are such as are used in the small observatories 

 of the amateur," to which they are in general equally adapted, 

 as to the service of the gendeman who may travel to foreign 

 parts. Of those, the two I have named in the tide, are the 

 most approved of for these purposes; and to draw up a com- 

 parison of their respective constructions and merits, is what 

 I have chosen for the subject of this communication. Were 

 I able to treat it as it deserves, I should entertain no doubt of 

 its coming wthin the views of this Society, nor of its useful- 

 ness ; particularly in assisting those, who may not already have 

 become acquainted with the different kinds of instruments, in 

 the selection of such as may be best suited to their purposes. 



The repeating circle, till wiUiin these few years, has been 

 very little used in this country, and in truth its merit but ill- 

 appreciated ; facts however are not wantmg, although dispersed 

 and insulated, sufiicient to remove all prejudice; particularly 

 experiments recendy made, with a small instrument of this kind, 

 at the principal stations of our grand national survey. On 

 the continent of Europe, where the art of graduation is not so 

 successfully cultivated as it is with us, an instrument which of 

 all others depends the least upon accuracy of division, could 

 hardly escape being too much commended: be this as it may, 

 observations lately made on the other side of the British chan- 

 nel, simultaneously with those used in the survey mentioned 

 above, have I believe given the best inforaied of all parties a 

 more correct idea of what may be expected from this instru- 

 ment. T 1 • 1 T T 



The altitude and azimuth instrument has 1 thmk been al- 

 most exclusively made in this country: many of them have 

 been sent abroad, but from their not havmg been used in great 

 national operations, the advantage of them has seldom been 

 made known to the world. Nearly the same may be said of 

 those which remain at home ; for aUhough some of them have 

 been much and skilfully used, yet owing to their having been 

 only in the hands of private mdividuals, who had no common 

 medium of communication, the labours of those who possessed 

 them have hitlierto been almost lost to astronomy. From this 

 general remark I must however except tlie observations of the 

 ae brightest fixed stars, which Mr. Pond made at Westbury 

 with a'^ao-inch circle of this kind, and which appeared m the 

 Phil. Trans, for 1806. This indeed was tlie first thmg (not- 

 witlistandiug some doubts and surmises from abroad) that un- 

 equivocally demonstrated a change of figure in the Greenwich 

 (juadrant, and subsequendy led to the procuration ot new in- 

 struments for our national establishment. 



The repeating circle has by no means failed for want of 

 Vol.60. No. 291. Jr^/y 1822. B publicity; 



