612 



SUMMARY OF CURRENT RESEARCHES RELATINQ TO 



The subsidiary leg, which carries the mirror, folds against the leg 

 of the tripod to which it is attached. The stage is removable, leaving 



Fig. 93. 



a ring, which is attached by three supports to the tripod, and rises 

 and falls somewhat as the tripod legs are shut or opened. 



The instrument is hardly so convenient as the modern forms which 



Fig. 94. 



have been devised in such profusion, but it is interesting as being a 

 very early progenitor of this class of instrument. 



