410 TRANSIT OF VENUS, 1874. KERGUELEN ISLAND. OBSERVATORY BAY. 



Adopting "W S as the standard, the following values result : 



which have been applied to the " Clock Slow " determined by observation, as 

 given in Table V. 



THE ALTAZIMUTH OBSERVATIONS. 



The Altazimuth used at Observatory Bay was constructed expressly by 

 Messrs. Troughton and Simms, and is a model of stability and good work- 

 manship. It was intended to measure both azimuths and zenith distances. 

 The rotating body of the instrument, including everything necessary for the 

 measurement of zenith distances, is similar to the vertical circles used at 

 Honolulu and Rodriguez (already fully described), with the addition of the 

 four microscopes for reading the fixed horizontal circle, the arms supporting 

 these being cast in one with the rotating body. The reticule contained five 

 vertical and five horizontal wires of spider's web. The observed zenith 

 distances being of stars for latitude, only the central horizontal wire was 

 used. The upper zenith-distance level was graduated with 72 divisions, and 



