18 



PROCEEDINGS OF THE AMERICAN ACADEMY 



sun. The two graduated circles would then give solar distances, and 

 the angle from the vertical plane through the sun, instead of altitudes 

 and azimuths. The second of these angles will be called the meridian 

 distance, and will be regarded as positive to the right, and negative to 

 the left of the sun. Of course, the direction of the axis should continu- 

 ally change, so as to follow the sun ; but as great accuracy in the 

 determination of the angles was not needed, it was found sufficient to 

 readjust it every few minutes. Another advantage of this arrangement 

 was, that the line of junction, being turned parallel to the axis, would 

 always lie in the plane passing through the sun, and hence be parallel 

 to the plane of polarization. Table XI. gives the result of five series 

 of observations made in this way : — 



TABLE XI. 

 Sky Polarization. Points equidistant from Sun. 



