NOTES AND CORRESPONDENCE. 
On Microphotography with High Powers—In the ‘ Quart. 
Journal of Microscopical Science’ for July, 1865, Vol. XIII, 
p. 249, I notice an interesting letter on a new method of 
illumination, by Count Francesco Castracane, who proposes 
the use of monochromatic light, by “the employment of one 
of the component rays of the solar spectrum, which was made 
to fall on the mirror of the microscope.” It appears, also, 
from this paper and the accompanying editorial remarks, 
that Count Castracane has succeeded in obtaining a good 
photograph of Pleurosigma angulatum, in which the minute 
markings on the frustule appear as hexagons. 
I take pleasure in confirming the statement thus made as 
to monochromatic light, and especially would mention the 
advantages of violet light for microphotographic purposes. 
For some months before I read the paper above referred to 
photographs had been successfully made by Dr. Edward 
Curtis, Brevet-Captain U.S.A., in the Army Medical Museum, 
with all powers up to 1000 diameters, the illumination being 
the direct rays of the sun reflected on the microscope mirror 
by a heliostat, and the pencil thus obtained being thrown 
through a cell containing a solution of the ammonio-sulphate 
of copper before falling on the achromatic condenser. 
To obtain the full effect of the violet light, however, the 
objective should be photographically corrected, that is, in 
determining its curves the index of refraction of the violet 
ray should be considered, and not that of white light. With 
such a lens the actinic and visual foci coincide if violet light 
is employed. Several such lenses, of excellent quality, have 
been constructed for the museum by W. Wales, of Fort Lee, 
New Jersey. A brief note on this subject was published in 
my report to the Surgeon-General, October 20th, 1865, “On 
the Extent and Nature of the Materials available for the 
Preparation of a Medical History of the Rebellion’ (see p. 148, 
circular No. 6, Surgeon-General’s Office. 
