280 F. ADDEY ON MEASUREMENT OP VERTICAL DIMENSIONS OF 



bottom of the cell, since the bottom of the cell will appear to be 

 at Pj, the apparent depth which we obtain by the readings of the 



fine adjustment will only be -th of the true depth, and our 



observed result must therefore be multiplied by n to obtain the 

 true depthi 



Fiq. 3 



Fig. 2 



Fig. 4 



/ / 



// /A/ ^A' / ' V \ 







\'7 



^^ik'.'//,- 



Fia 1. — Path of a ray from mounting medimn to air ; no cover glass. 



Fig. 2. — Body immersed in mounting medium ; no cover glass. 



Fig. 3. — Path of a ray from mounting mediiim through cover glass 



into air. 

 Fig. 4. — Body immersed in moimting mediiim and provided with cover 



glass. 



Consider now a body of vertical thickness li immersed in the 

 medium (Fig. 2). 



If ^1 and ^2 be the true distances from the surface of the liquid 



