sentially, their processes consist respectively of separating the
fluid portion of the white of egg, and adding thereto a weak solution of
the iodide of potassium. This is floated over a clean glass plate, so as
to cover it with a very thin film, and carefully dried. When this is
completed, the prepared surface is dipped into a solution of nitrate of
silver, and thus an iodide of silver is formed on the surface. This
iodide of silver being washed, as in the calotype process, with
gallo-nitrate of silver, is very sensitive to the solar radiations, and
being placed in the camera-obscura, is speedily impressed with a dormant
image, which is developed by the deoxidizing action of gallic acid." A
good steam gauge has long been a desideratum. All kinds of portable
gauges are, either not to be depended upon, or subject to frequent
repairs; so much so, that by law every steam-engine used in France is
provided with a gauge on the barometer principle, that is 10 feet, 15
feet, 20 feet high for a steam pressure of 60 pounds, 90 pounds or 120
pounds to the square inch. Mr. Bourdon, chief engineer at the Creusot
works, where the engines of the frigate Mogador, were built, has devised
a gauge, which has obtained for him a medal at the London Fair, and is
highly spoken of. It is based upon the fact, that a thin metal tube,
coiled up and subjected to internal pressure, will tend to uncoil itself
in proportion to the amount of the pressure. The tube used is first
flattened preparatory to the coiling up, so as to render this operation
more easy. One of the extremities communicates with the boiler, the
other is pointed and turned up so as to serve as an index on a circular
scale. The apparatus is fixed in a case, in the shape of a hair
medallion, and closed with a glass. Experiment must show if the effects
of temperature be insignificant compared with those of pressure, and if
the internal working of metallic atoms will not in time make this gauge
give wrong indications.--If the instrument can bear the test of
practical use, it will soon supersede every other already known. The
inventor has already been rewarded by a council medal at the London
Exhibition, and the cross of the Legion of Honor in France. In the last
named country, the Government has made provision to try it on all the
railways.

* * * * *

Experiments have been made on the Paris and Lyons Railway for the
application of electromagnetism to lo