SCIENTIFIC SUMMARY. 
223 
-cut, and haying fitted into one portion of this sphere a plate of very thin glass. 
This chimney is lined 'with a fine layer of white plaster of Paris, and when 
placed upon the lamp no glass chimney is required. Its advantages are, 
firstly, that a stream of parallel rays of the whitest “ white-cloud ” light is 
thrown upon the mirror of the microscope. Secondly, that all light is cut 
off, save that which reaches the mirror, thus protecting the worker’s eyes. 
Thirdly, that being of copper, there is no annoyance of broken chimneys. 
There are other peculiarities in this chimney which we have not yet 
noticed j one is, that by a process, which Mr. Collins has not yet made 
known, it is composed of one continuous piece of copper, without seam or 
union, and the other that the plaster of Paris, by absorbing the products of 
combustion, formed in low temperature by petroleum, enables the flame to 
be retained at a lower level than in ordinary lamps. We examined this 
new piece of accessory apparatus, and can speak most favourably of its 
qualities and usefulness. 
PHOTOGEAPHY. 
Improvement in Dippers. — The third number of the Illustrated Photographer 
contains an improved form of glass dipper, devised by Mr. J. C. Leake, 
to avoid a very common source of failure arising from the nitrate solution 
being retained upon the tranverse ledge on the strip of glass forming the 
dipper. Mr. Leake thinks it probable, that when the coated plate is set into 
this little pool of silver-solution, a great part of the nitrate is at once ab- 
stracted by the iodides contained in the collodion ; and as there is no solution 
to keep up the supply, wherever the weakened solution reaches the film, the 
cotton is precipitated, or the film is in some way altered in character, and 
cpaque markings, radiating out all over the film from the bottom of the 
plate are produced. These annoying stains were, however, entirely got rid 
of by altering the dipper, and substituting for the ledge two square pieces of 
glass fastened on, as seen in the diagram. 
Collodion Prints. — Much attention is being given to the process of printing 
from negatives on wet collodion in the copying camera, and afterwards trans- 
ferring the films to plate paper. Prints so obtained are more delicate in 
detail and gradation, and more permanent, while they can be produced with 
considerable rapidity. The collodion used should give a strong film. The 
print is toned by mercury, and when mounted placed under a copper plate 
and rolled. 
New Walking-Stick Tripod. — In our last Summary we described a new 
•opera-glass pocket camera, devised by Mr. Sutton, and stated that a pocket 
tripod stand might be contrived for it. This has not yet been done j'but in 
the third number of the Illustrated Photographer, a very ingeniously con- 
trived walking-stick tripod, suitable for this camera, is described by J. S. 
We give a diagram of it. A is the top part of the stick, 1^ inch diameter 
and 9 inches long, with' a hole through it i inch diameter ; B is a rod ^ 
inch diameter, and 15 inches long, to go through the top part of the stick A, 
and 6 inches down into the legs of the tripod. The legs are hollowed in the 
