On the use of wide illuminating cones in the microscope.

In bright-ground illumination, glare is noticeable when the condenser aperture is equivalent to that of the objective. It can still be detected, though to a greatly reduced extent, after most causes of glare have been avoided. It is suggested that this residual glare is inevitable, and represents the loss of contrast resulting from a relative excess of direct rays, which occurs when the direct light falls in the marginal zone of the objective, since half of the diffracted rays then falls outside the lens.