38 HI. M. Parkhurst on the Photo-mapper. 
so determined that photometric accuracy shall not be sacrificed, 
e 
deed a plain Bar Photometer ea 
By a still further modificatio 
may be produced, by means of i 
key of my star-mapper; and this constitutes the Photo-mapper, 
which I will now more particularly describe. 
being seven-eighths of the distance from the object-glass to its | 
focus, the length of the supporting bars is seyen-eighths of the 
radii uae 
