Total Eclipse of August 7, 1869. 



181 



merit could be used. A brass tube beld in position by a set 

 screw, was fitted over the eye-piece, to which was attached 

 a disc of brass, three and a quarter inches in diameter, in 

 which was set six plates of glass of different colors and 

 density. 



This apparatus is here represented, on a scale two-thirds 

 the full size. The colored glasses are marked, b, c, d, e, 



/, and g. The latter was provided with a cap, for holding a 

 double or triple glass. The position of the eye-piece is at 

 a. "When in the position here represented, no colored 

 glass is over the eye-piece. The set screw, for clamping to 

 the eye piece tube, is at A. In order to bring any one of 

 the colored glasses over the eye-piece, the plate is revolved 

 about the centre o. By this arrangement, any color can 

 almost instantly be brought before the eye. It has been 

 surmised from the observations of previous eclipses, that 

 perhaps the color of the glass used, might materially 



