"WHEELER SECONDARY BASE IN GEODETIC SURVEYS. 25 



From the three, probable error z=: i in 194,000 



" two latter, " " =z i in 533,000 



Trovers Pt. Base {Mon.) 1885. 



Ft. Mean Temp. 



1st measurement, on cool, smoky day r= 9711.916 ( 61°. 3 ) 



2d " by twilight = .915 C 62°.8 ) 



3d " by lamplight =z .892 ( 5i.°2 ) 



From all, probable error zrr i in 1,920,000 



" two latter, " " z= i in 1,250,000 



Glasgow Base (Mo.) 18S5. 



Ft. Mean Temp. 



1st measurement, by day, sun in last part r= 7923.237 ( 45°. 6 ) 



^d " by day, sun in first fart z=z .403 (52°.!) 



Probable error z:= i in 140,000 



But taken in parts (as noted at time of measurement), we have 



Ft. Mean Temp. 



1st 15 tapes of ist measurement, overcast sky .... ■=r 4485.635 (42°.! ) 



and II " " 2d " " " .... — 3437.709 (49°-3) 



Total Base r^ 7923 344 



which agrees closely with the mean of the above, and is a very 

 reliable value for the base. 



Beverly Base {Mo.) 1885. 



Ft. Mean Temp 



ist measurement, by day (hazy sky) nr 7933 803 ( 79°. 5 ) 



2d " by lamplight :r= .797 ( 65°.5 ) 



3d " by lamplight =r .821 ( 58°. 8 ) 



Probable error r= i in i,6co,ooo 



The two measurements of the known half of the Olney Base 

 {primary 1879) gave results agreeing within .04 of an inch, or 

 practically identical results. It is i in 3,250,000. 



But it is possible to determine the probable error in measure- 

 ment, and also that for the standard tape from the discrepancies 

 on the zinc strips. Tn the following table, 2d column gives the 

 direct differences in inches as read from each zinc strip ; 3d col- 

 umn, discrepancies due to expansion and errors of observation, 

 and 6th column gives the same corrected for expansion. The 



