NOTES AND CORRESPONDENCE. 
I RECEIVED lately a letter from Count France Castracane, 
in which he desires me to forward to you the following 
remarks on the Woodward observations reported in the 
‘ Quart. Journ. Mic. Sci.’ for July, 1866. 
“T quite agree,” he says in the beginning, ‘‘ with Mr. 8. 
J. Woodward, that for microphotographical uses one may 
- obtain nearly the same results with any undecomposed ray of 
light which has been transmitted through a solution of 
ammonio-sulphate of copper; and I am equally persuaded of 
the usefulness of microscopical objectives ready made to 
obtain the coincidence of the action with the visual forms. 
The usefulness of a hight modified by traversing a coloured 
medium has been pointed out on other occasions ; and M. 
Bruster has lately suggested to illuminate the microscope with 
alcoholic light, saturated with chlorine of sodium. Such is 
the opinion, too, of Dr. Noiterrier (p. 180 and following of 
his very useful book ‘La Photographie appliquée aux 
Recherches Microscopiques,’ lately published in Paris by 
Baillicre et fils.) 
From the application of decomposed light to photography, 
I expected, indeed, a great advantage, which I did not 
obtain, as I tried to take any microscopical object illuminated 
with a violet ray resulting from the sun-light decomposed by 
an enormous prism, and sulphuretted carbon, which I had 
constructed on purpose. Nevertheless, I cannot but insist 
upon the usefulness of illumination with decomposed and 
vigorously microchromatic light, which may be obtained 
only with a good prism, seeing that the cobalt glass and the 
solution of ammonio-sulphate of copper admits with the violet 
some part of other rays, so that we can never obtain an abso- 
lute correction of the chromatic aberration, which it is known 
cannot be obtained by any combination of lenses, no matter 
how perfect they may be. 
