Lacroix ’ Axial Goniometer .— Winchell. 
79 
LACROIX’ AXIAL GONIOMETER. 
By N. H. Winchell, Minneapolis, Minn. 
The measurement of the angle of the optic axes is one of 
the essentia] operations in the investigation of a mineral, as 
this property is frequently a characteristic criterion for its 
determination. Yet the accurate determination of this angle 
has alway been done by special and often large instruments, 
which necessarily can be found only in the best equipped 
mineralogical laboratories. The construction therefore of a 
simple device for making this measurement is an addition to 
the resources of the ordinary petrographer, and is welcomed 
by every one interested in the microscopic study of minerals. 
Fig. 1. 
