296 ILLINOIS STATE ACADEMY OF SCIENCE 



the incident ray, it is readable to a good degree of ac- 

 curacy. 



EXPEBIMENTAL DATA AND CONCLUSIONS. 



Number 



of moving Angle Angle emergent B 



reflections mirror moved ray moved — N x 2 



N 



7 



9 



11 



By utilizing the optical lever, the emergent ray is 

 converted into a measurable quantity even with .0001° 

 angular displacement of the moveable mirror, using 

 eleven reflections. 



By using the two mirrors on moveable systems, an 

 angular displacement of .00005° can be measured. 



CONCLUSIONS 



One-fifth of a second of arc is measurable with high 

 precision by this method, and it seems not an improba- 

 bility to refine it to measure much smaller displacements. 



