58 



MICHIGAN ACADEMY OF SCIENCE. 



I have examined the wire inclination during the periods 1898, May 23.4 

 to June 14.8 iiirlusivp. niul December 10.3 to December 27.8 inclusive, 

 taking account of the change of refraction during each day's observation. 

 Calling the effect of the incliijation of the horizontal threads cos S sin t. I, 

 where t is the hour angle and / the inclination, the values of I for the 

 two periods as determined from Polaris are: 



TcJescopc clamp c<i.sf, Pohnis direct, East zenith distances too great, 

 or E. ends of threads too high. 



I8y8 



Miiy ■-'3.4 



Zi.9 



•ib 4 



2.V9 



2t).y 



30 3 



30.8 



Juue 1.3 



•i» 



y. 4 



K X 



n .T 



S'jni 



Mean 



1898. 



December 10.3 



12.8 



13.3 



13.8 



153 



15.8 



17.3 



18.3 



24.3 



27.3 



27.8 



Sum 



Mean 



—90.5" 



+ 146.2 

 + 176.0 



+ ?;0 4 



+59.0 

 + 152.6 



-26.5 

 +159.0 

 +224.1 



+74.5 



-h64.6 



+ 969.4' 



+88.1" 



16. — Prohahle Error of Single Pointing on Polaris. 



If it is assumed that the value of I for the first period referred to in 

 article 15 is 58.4'', and for the second period 88.1", it is possible to com- 

 pute the probable error of a single pointing for each date taken separate- 

 ly. The nadir used on each data is the mean of the observed nadirs, and 

 the reading of the circle is included with the pointing. 



Probahle en or of a single pointing on Polaris. 



1898 



May 23.4 



24.9 



25.4 



25.9 



26.9 



30.3 



30.8 



June 1.3 



2.8 



3.4 



6.8 



14.3 



1898. 

 December 10.3 

 12.8 

 13.3 

 13. H 

 15.3 

 15. i< 

 17.3 

 18.3 

 24.3 

 27.3 

 27.8 



Number 

 pointings. 



Probable 



error 

 pointing. 



±0.40" 



±0.45 



±0.43 



±0.29 



±0.08 



±0.22 



±0.27 



±0.33 



±0.37 



±0.52 



±0.35 



The probable error of a single pointing is taken as ± 0.33". 

 For the mean of 7 pointings the probable error is ± 0.13". Compounding 

 this with ± 0.20", the probable error of the mean of two nadir determina- 



