ULTRAMICROSCOPES 75 



with the two front lenses will cling in place. The illuminating 

 beam will pass through this drop in the focal plane of the objec- 

 tive O. The image resulting upon focusing the microscope will 

 appear to be two hazy triangles of light united at their apices by 

 a more or less marked brighter thread or band. In this band 

 are seen the diffraction disks due to the infinitely small particles 

 in suspension. By means of the ocular diaphragm all of the 

 hazy triangles are cut off and the connecting thread or band of 

 light alone allowed to appear in the field of view. 



