426 Scientific Intelligence. 
ascertain what would be the effect of the interfoliation of lamine 
in which the planes of the two sets of optical axes had the same 
relative position as in the several members of the macle. To that 
end I divided a plate, which represented the largest optical angle 
I had observed, into as thin lamine as possible, and then superim- 
was nearly equal—that a symmetrical ring system was obtained, 
in which the optical angle was about 13°,—the smallest I had 
measured; and, by varying the relative thickness, intermediate 
degrees of optical divergence were produce y now introduc- 
apparent variation of optical le I had observed in the plates 
bolas proportionally indefinite. I therefore next made a re 
ent 
vention of balsam, and in alternating positions, like the members 
rings, such as the ; 
repeating now this experiment with a Muscovite mica having 
wide optical angle about 63°, I obtained a most remarkable and 
