4.18 Zach 0)1 licpeating Circles. 



with such accurate divisions*, or such powerful telescopes, as 

 those larger instruments possess, that arc furnished for fixed 

 observatories." 



This is precisely what we said in the first number of the 

 sixth volume, page 63, of our Correspondauce .htronomique : 

 " We beheve, nevertheless, that repetitions may be of infinite 

 use in the small circles used in travelling, the divisions of which 

 cannot go higher than ten seconds." 



We believe, above all, that the repeating theodolites of 

 M. Reichenbach's construction are superior to every other in- 

 strument, even to repeating circles, for observations of the 

 azimuths and of terrestrial angles, because such observations 

 are always made on a horizontal plane ; and with these small 

 and very portable instruments, though their divisions be only to 

 every ten seconds, we can succeed in obtaining the exact se- 

 cond, as our readers may convince themselves by casting an 

 eye over our observations of the azimuths and over the terres- 

 trial angles given in our work, U Attraction des Montagiies. It 

 is also well known that the repetition of horizontal angles does 

 not present those anomalies which are observable in the re- 

 petition of vertical angles. Of this we have suggested the 

 probable reason in the Number just quoted (p. 64). 



A celebrated London artist has said that he had heard that 

 some of his contemporaries wei'e endeavouring to bring to per- 

 fection repeating instruments, but that he advised them to do 

 nothing of the sort, but rather to employ their time and talents 

 in the construction of instruments which promise more success, 

 and to endeavour to bring to perfection the art of dividing. 

 But it appears to us, that this artist is mistaken if he imagines 

 that the only use of repetition is to correct the defects of divi- 

 sion ; it is also of use in correcting the smallness of the in- 

 strument, defects of the level, defects of the telescope, defects 

 of observation, &c. It appears that his celebrated con- 

 temporary DoUond has a more accurate perception and a 

 sounder judgement concerning the principle and the nature 

 of repetition ; and we hope that the excellent artists with 

 which London abounds will continue to improve this kind 

 of instrument as well as every other. It is no less desirable 

 to serve the humble retreats of modest amateurs, than the 

 sumptuous observatories established by imperial and royal mu- 

 nificence. Every be dy cannot procure 8-foot circles and 1 5-foot 



* The divisions of this 15-inch repeating circle are for every 10". 

 Lenoir's of the same distance for every 20''. Reichenbach's 12-inch for 

 every 4". 



sectors, 



