{8"c 

 "c 



48 TRANSIT OF VENUS, 1874. HONOLULU. 



The several determinations of the zero of the micrometer are 



9 r< 891 from the first series of double-diameters. 



10 r -163 from the limb measures between 20 h . 53 m . 59 s . and 20 11 . 56 m . 40 s . 

 10 r -100 from the limb measures between 21 h . O m . 40 s . and 21 h . 3. 21 s . 



9 r> 956 from the second series of double-diameters. 



For the reduction of the measures of Cusps the zero has been taken as 

 9 r -89l ; and the value of s, 3 r -517. 



For the limb measures the zero has been taken 10 r -130; and s, 3 S -490. 



.ff=976"-8o r = 3i"- 4 2. 



8"'g32 + 286 8 r for cusp measures. 

 . g" - oo2 + 286 8 r for limb measures. 



Assumed astronomical latitude 21. 17'. 56"'3 N. 



longitude west of Greenwich 10 h . 31 m . 27 S '3. 



Similarly for Mr. Nichol's observations with the 4^-inch equatorial, we 

 have, from the first series for diameter of Venus, 



s = 2 r '448 

 and zero 9 r '9g6 for the direction parallel to the Sun's limb. 



and for the second series 



s = 2 r '434 

 zero io r> ooo (direction not stated ; probably parallel to Sun's limb), 



J i2" - 835 + "410 S r for cusp measures. 

 an f> - ^ I2 "-gi3 4. -410 8 r for limb measures. 



The equations of distance of centers of the SUN and Vvnm for every obser- 

 vation with both instruments are exhibited in the following Tables B and C, 

 (which also give the time of contact deduced from each micrometer measure 

 of cusps,) taking the tabular semi-diameters as above, and assuming the 

 mean solar parallax to be 



'. ' ' S -; 8"-950 (1 + ,-~). 



The relative weights assigned to the cusp measures are arbitrary. The 

 model practice proved that the measures taken in the last two minutes were 

 about twice as accurate, for the object in view, as those taken between five 

 and three minutes from contact. 



