1867.] 



for the Verificatiofi of Sextants. 



5 



is evident that by this means we shall eliminate any error of graduation 

 of the theodolite. 



A complete set of determinations of these angular distances ought, 

 therefore, to refer to at least three starting-points in the horizontal 

 circle of the theodolite, these being, say 120°, apart from each other. 



The following complete sets have been made at various dates by Mr. 

 G. Whipple:— 



Measurements of the Angles between the Collimators of the Apparatus 

 for the Yerification of Sextants. 



The measurements were made with a 6-in. Theodolite, divided to 30". 



Table I. 



Angles 

 between 

 collimators. 



Dates of Observation, 



^oy. 23, 1866. 



Nov. 26, 1866. 



Feb. 27, 1867. 



May 2, 1867. 



Means. 



iNos. I and 2 . . . 

 1 » 3-" 



» I „ 5- 



29 59 44'4 

 59 59 317 

 105 1*7 

 120 117 



29 59 35'o 

 59 59 417 

 105 i'7 

 120 117 



29 59 45'o 

 59 59 467 

 104 59 417 

 119 59 567 



29 59 267 



59 59 29-3 

 104 59 467 



"9 59 53'3 



29 59 37-8 

 59 59 37'3 

 104 59 52-9 

 120 3'3 



Table II. 



Differences from Means. 



+0 6-6 

 — 5"6 

 4-0 8-8 

 +0 8-4 



-0 2-8 

 4-0 4-4 

 -f 8-8 

 + 8-4 



4-0 7-2 

 4-0 9-4 



— II"2 



-0 6-6 



— I IT 



— 8-0 



— 6-2 



— lO'O 



Table III. 



Angles 



between Collimators. 





Nos. 4 and 5 





/ 

 15 



10-4 



)> I » 2 





29 59 



37-8 



» 3 4 





45 



15-6 



„ I „ 3 





59 59 



317 



„ 2 „ 4 





75 



15 I 



„ 2 „ 5 





90 



25-5 



„ 1 » 4 





104 59 



52-9 



» I „ 5 





120 



3-3 



It will be seen from Table II. that the observational differences from 

 the means are extremely small, and capable of being accounted for by 

 the uncertainty of reading a theodolite graduated to 30". "We may 

 therefore suppose the positions of the collimators to have remained the 

 same throughout the period embraced by our observations. 



