NOTES AND CORRESPONDENCE. 
Sunlight Illumination of Diatoms.—Dr. Maddox (whose skill 
and success in obtaining micro-photographs is well known) 
remarks, in a letter to me, dated 28th July, “I have seen in 
the photograph what I never saw in the object with the most 
careful illumination.”’ Some years ago, in one of my com- 
munications to the Society, ‘On obtaining Photographs of 
Microscopic Objects,” I mentioned the very peculiar distinct- 
~ ness with which markings on test-objects were shown on the 
screen, and expressed my opinion that the photographs might 
aid in determining their structure. Dr. Maddox’s remark 
having revived this impression, | placed my microscope in 
strong sunlight—illuminated the object with the concave 
mirror and an achromatic condenser of large aperture. As 
a consequence, the illumination was so intense that no object 
could be looked at directly through the microscope, as the 
eye would not endure the light for an instant. To look for 
markings was precisely hke attempting to discern spots on 
the sun’s disc through a telescope without the protection of 
sun-glasses; but by taking the red and green glasses off my 
sextant (which, combined, gave a pleasant neutral tint to the 
sun), and laying them on the caps of the eye-pieces, the light 
was toned down to just the right pitch, and the markings on 
all the most difficult tests were easily and quickly brought out 
with remarkable distinctness. In objects of extreme difficulty 
the parabolic dispenser may be employed, directing the sun- 
light with the plane mirror. With the achromatic condenser 
and direct sunlight, the sap circulation in Anacharis is beau- 
tifully shown. 
I feel that some apology is due for the smallness of this 
announcement, but as many who use the most costly micro- 
scopes aud apparatus appear to use them principally for the 
purpose of displaying the markings on the most difficult tests, 
to these anything should be welcome that will aid in stimu- 
lating or coaxing an expression into the reluctant aspect of 
