54 TRANSIT OF VENUS, 1874. HONOLULU. 



By obtaining independent values of a revolution of the screws of the 

 micrometers, the terms depending upon or in these equations may be 

 eliminated. With this view the distance of the Model from the stage was 

 measured three times with a 100-feet measuring tape, the face of the model 

 being placed exactly 800* feet from the front edge of the table on which the 

 telescopes were laid. These projected a little over the edge, so that the 

 distances of the object glasses from the Model may be taken at 



798*4 feet for the 6-inch telescope. 

 799' 6 4^-inch 



The diameter of the disk of brass representing Venus was measured many 

 times with three different scales by TROUGHTON and SIMMS, with the following 

 results : 



2-85g4 inches (by a scale of T ^). 

 2-8570 ( -jifr). 



2-8552 ( millimeters). 



The mean 2-8572 inches. 



The mean of a great many measures of the diameter of the model planet 

 as seen in the telescopes gave the apparent values 



6 r- 76o -020 for the 6-inch instrument. 

 4 r '76o -oio ,, 4^-inch 



Consequently the values of one revolution of the screws, for the focus cor- 

 responding to the distance of the model, are 



g"-O99 -o3o for the 6-inch. 

 i2"-8g7 -027 for the 4^-inch. 



The focal lengths of the object glasses being, respectively, 89 and 69 inches, 

 the values of one revolution of the screws for the solar focus are 



g''-i84 for the 6-inch. 

 i2"-g8g for the 4^-inch.f 



"We have, therefore, the following values of the true semi-diameter of 

 Venus : 



With the 6-inch instrument 32"- 18. 

 4^-inch 3i"'7i. 



Hence the value of 8 r is 



+ o"'76 for the 6-inch. 

 + o"-2g 4^-inch. 



* Mr. Gay, with the 66-feet chain, afterwards made the distance 802 feet by a single measure. 

 I doubt the accuracy of this. 



f I afterwards found by transits of the double image of Polaris the values I2"'99 and i3"'O2. 



