GEOMETRICAL MEASUREMENTS 173 



which may be tilted (Ochiallini). This device does away with errors 

 originated from micrometer screws. To the observation system is 

 adioined a reading device, next to the eyepiece, in which the micro- 

 meter scale is also shifted by a parallel-sided plate. Provided the 

 thickness of the second plate exceeds that of the eyepiece and for 

 an identical rotation of both plates, the micrometer motion is more 

 extensive and measurements more accurate. 



An electrical measuring and recording device may be added to 

 this device. Rotations of the eyepiece plate take effect direct on an 

 electrical system that feeds them to an electron computer. High- 

 precision microscopes are now built by several large concerns. These 

 instruments, currently used in nuclear research, should likewise, prove 

 verv useful to biologists. 



