* * * * *

PORTABLE ELECTRIC LIGHT.

The famous house of MM.  Sautter, Lemonnier & Co. takes a conspicuous part in the Paris exhibition, and from the wide range of its specialties exhibits largely in three important branches of industry:  mechanics, electricity, and the optics of lighthouses and projectors.  In these three branches MM.  Sautter, Lemonnier & Co. occupy a leading position in all parts of the world.

The invention of the aplanetic projector, due to Col.  Mangin, was a clever means of overcoming difficulties, practically insurmountable, that were inseparable from the construction of parabolic mirrors; this contributed chiefly to the success of MM.  Sautter, Lemonnier & Co. in this direction.  The firm has produced more than 1,500 of these apparatus, representing a value of nearly L500,000, for the French and other governments.

Besides the great projector, which forms the central and crowning object of the exhibit of MM.  Sautter, Lemonnier & Co. in the machinery hall, the firm exhibits a projector 90 centimeters in diameter mounted on a crane traveling on wheels, in the pavilion of the War Department.  The lamp used for this apparatus has a luminous value of 6,000 carcels, with a current of 100 amperes; the amplifying power of the mirror is 2,025, which gives an intensity of ten millions to twelve millions of carcels to the beam.

Projectors used for field work are mounted on a portable carriage, which also contains the electric generator and the motor driving it.

[Illustration:  MILITARY PORTABLE ELECTRIC LIGHT AT THE PARIS EXHIBITION.]

It consists of a tubular boiler (Dion, Bouton & Trepardoux system).  This generator is easily taken to pieces, cleaned, and repaired, and steam can be raised to working pressure in 20 minutes.  The mechanical and electrical part of the apparatus consists of a Parsons turbo-motor, of which MM.  Sautter, Lemonnier & Co. possess the license in France for application to military and naval purposes.  The speed of the motor is 9,000 revolutions per minute, and the dynamo is driven direct from it; at this speed it gives a current of 100 amperes with and from 55 to 70 volts; the intensity of the light is from 5,500 to 6,000 carcels.  The carriage upon which the whole of this apparatus is mounted is carried on four wheels, made of wood with gun metal mountings.  These are more easy to repair when in service than if they were wholly of iron.  The weight of the carriage is three tons.—­Engineering.

* * * * *

ELECTRIC MOTOR FOR ALTERNATING CURRENTS.