NOTES AND MEMORANDA. 
295 
which the change of distance between a and c, required in giving the 
correct focus, may be obtained. The base e, f is attached to a second 
or under base g, h by a hinge at h, which allows the end e ot the 
movable base e, f to be raised to any required angle, at which it may 
be maintained by the block at So convenient and compact is this 
lantern, that it may easily be stowed away in a small trunk. 
When a series, of objects of different sizes is to be projected, as is 
the case with microscopic photographs taken under the same adjust- 
ments, it is, as we have said, a great gain in the projection of small 
objects if the circle of light used for illumination is reduced, and at 
the same time increased in brilliancy. This is accomplished in the 
above arrangement as rapidly as can be desired by removing d, c 
together along the slide of the base e,f to a sufficient distance from 
the face of the condenser Ji to allow the convergent rays of the latter 
just to cover a circle which will include the object to be projected. 
The greater intensity of the illumination thus obtained renders the 
definition of fine markings or other peculiarities on small objects as 
clearly visible at considerable distances as are the coarser markings 
on large objects under a weaker light. 
In closing this brief communication, I desire to add that I made 
photographs of Frustulia Saxonica under a power of 7000 diameters. 
The photographs in question were made in the City College building, 
by a Y^-inch immersion Beck lens. The light was from the sun, 
reflected by a heliostat through ammonio-sulphate of copper solution 
and condensed on the object at an angle of 30° to 40°. The jjhoto- 
graph in question was direct, by which I mean that there was no 
intermediate or secondary enlargement of a first photograph. With 
this photograph and the lantern described I have shown Frustulia 
Saxonica magnified more than half a million diameters, a result which 
must be seen to be apj)reciated. 
Cleaning Slides and Cover -glasses. — Mr. C. E. Hanaman, of the 
Troy (U.S.) Scientific Association, recommends as being as efficacious 
as the nitric acid bath, and wholly free from its disagreeable odours, 
a cold saturated solution of bichromate of potash in w'ater, to which 
about one-eighth of its bulk of strong sulphuric acid is added, the 
mixture being made in a porcelain or thin glass vessel, as the heat 
