1072 



KECORD OF CURRENT RESEARCHES RELATING TO 



toucli of tlie rectangular motions, the iitility of the rotation is very 

 much curtailed ; a rotatory motion of the stage, unless it be approxi- 

 mately concentric with the optic axis, appears to us to be practically 

 useless. 



3rd. The Diatom stage (Fig. 136, half-size) is 2^ inches in diameter 

 and is bevelled out beneath, so that its thickness is only ^^ inch at 



Fig. 137 



the centre. The lower plate rotates in the ring of the stage, and the 

 upper one can be slipped backwards and forwards (beneath the spring 

 clips) in two grooves. The four adjusting screws for centering are 

 shown in the figure. Owing to its small size, it is very solid ; it is 

 especially convenient in that the swinging substage can be moved 

 almost to the horizon of the object. 



