LIMITS OF ERROR 53 



to the Government of the day. The aakry waa then 



1. thirty chaldron* of eoala and one hundred 

 poonda of wax candles" were aaked f . the 



enclosing of th- K garden) Evidently 



official mini I.,. -I n >t graaped the idea that 

 astronomer - royal waa i r a fortune-telling 



interpreter of the heavens, aa Kepler had been forced 

 to become for bread ' u -i one aaaiatant all - m-ht 

 work waa barely poaaible ! l Tlie instruments in oae 

 lie judged of from " An Ace juatorial 



Instrument," or " mural quadrant/' given to the Royal 

 Society in 1793, twenty yean aft- r II. rachel began 

 hia labours. The precision of observation among 

 the ancients could not be trusted to within from five 



i in in lit.- Tycho Brahe reduced the probable 

 limit of error to within <>m* minute, Hevelius in th.- 

 following century brought it down to fiften or twenty 

 secondhand in the ctM; was reduced to seven 



or eight seconds. 1 To tions to any 



credit it was then felt th.n a probable error of more 

 than a few seconds could not be admitted or perhaps 



.-i hiiM'hv.lth part uf the errors unavoidable in 



the days of Hipparchus. In 1827, Sir John Uerachel 



was able to say that he had " secured such a degree of 



-ion that the stars cross the wire often on th. 



very beat of the chronometer when they are expected/' 



insit instruments, mural-circles may be said 



to have been in th-ir infancy when H-rachel began 



his work. He did not propose to work or measure 



these as men do in an observatory. He was 

 eager to see with a telescope; but he soon found 



if he was to do any good, he would require to 



1 Wild, ii. 250. '/ML IVwMu for 1793. 



