1883.) 79 (Sharpless. 
The latitude was determined by pairs of stars, one of each pair being 
horth and one south of the zenith. The difference of the zenith distances 
was measured by the micrometer and the latitude calculated by the formula, 
“op = hCO+ 0) +342’) 
As a preliminary work the value of a revolution of the micrometer 
Screw was determined by observing the passage of a star between the wires 
Set at some known. distance apart, and multiplying the time by the factor 
15 x cos Dec 
Dist. between wires’ 
A. better result was obtained by the method of observing Polaris at 
time of greatest elongation. This time ‘I, and the zenith distance Z, were first 
calculated and the telescope set at the latter angle. About twenty minutes 
before T, the movable micrometer wire was set in front of the star and the 
time of crossing recorded on the chronograph ; the wire was then ad- 
vanced one-fifth of a revolution, and the time again noted, and so on forty 
times. From these were obtained twenty values of a revolution of the 
Screw. The computation is given in outline in the following table. The 
quantity Z— Z, was computed in each case by the equation : 
The mean of twenty-one observations was 111.67’. 
cos 3 
Zam 7, = gin (T— Tt. 
. sin 1// 
The level error was so slight that it was not taken into account ; 
No. Micrometer 1, py, ZimZigs 
Reading. 
6.80 er 50m. 18.88 BI BL 4B B.59 
2 6.60 Bl 16.2 na 1) 5.1 410,68 
8 6.40 52 33.2 ale TR AO eB TO 
4 6,20 58 34.2 ee aa a a BAD OO 
5 6. 54 AG, Out mae TG ce AO — 843.59 
ete. ete. etc. etc. 
24 2.80 6. 72 Oe se De eR a 
22 2.60 "8 16.4 Fr tance ot “. BOi19 
28 2.40 "4 ee ee OR OBR TC Uy hggeRs 
24 2.20 5 FEN 1 SAMI Saye Me die am ey (584 
2% 2, 16 Rd a ke RR Oe ian 
etc. ete. etc, etc. 
Comparing the 1st observation with 21st, the 2d with 22d and so on, 
and dividing the results by 4, we obtain for the value of a revolution of 
the screw by this method the following : 
111.'78 111.25 118.04 109.92 
112.20 110.71 113.98 112.66 
112.05 111.28 113.26 112.76 
110.'76 110.67 112.78 111.88 
111.08 111.59 112.25 111.16 
The mean of these is 111.//9 and this is the value employed in subse- 
