148 Progress of Invention. 



tion of enlarged images of opaque objects, such as photographs, 

 for the use of portrait painters, etc. It is reflected from a large 

 concave mirror through a nine-inch condensing lens ; and passing 

 thence to the object, -which is placed at an angle of 45°, it is 

 reflected to a double acromatic object-glass, which refracts it so as 



to form a picture on the screen intended to receive it. Aluminium 



bronze, consisting of ninety parts copper and ten aluminium, is used 

 with very great advantage as a casing for bearings which, when 

 ordinary materials are used, are liable to become heated, on account 

 of the high velocities of the moving parts. It was found to answer 

 admirably for a mandril, which made 7000 revolutions in a minute, 



and with which, every other bearing tried, had proved a failure. 



Electro magnetism has been applied by- Sir Charles Fox to the over- 

 coming of one of the greatest difficulties connected with railways, 

 namely, the want of sufficient adhesion between the driving-wheels 

 and the rails. For this purpose, deflected belts of insulated wire 

 are placed round the lower portions of the driving-wheels of the 

 locomotive, which, when these belts are connected with a galvanic 

 battery, become powerful electro-magnets that attract, and are 

 attracted by, the rails. As the wheels revolve within the belts, 

 their lower portions, for the time being, are always magnetic. The 

 belts are supported by slings, and steadied by stays, and are capable 

 of being connected together, etc.- — —It is supposed that the sudden 

 and spontaneous extinction of burning magnesium wire arises from 

 the presence of particles of oxide. Magnesium possesses no duc- 

 tility ; and hence, to form it into wire, it is forced in a fluid state 

 through holes in a steel die. This causes portions to be oxidized, 

 as the metal is highly oxidizable in the fluid state, and the particles 

 of oxide are incorporated with the wire. All inconvenience from 

 this oxide is prevented by adding to the magnesium lamp a spirit 

 lamp, through the flame of which the magnesium wire is transmitted 

 at a proper speed, by means of suitable mechanism. — —It has been 

 proposed to propel omnibuseSj etc., through Paris by means of a 

 motive power, which is to be derived from gaseous ammonia. It has 

 been calculated that if twenty kilogrammes of liquefied ammonia 

 are vaporized, and the vapours are received in sixty kilogrammes of 

 water, a power equivalent to that of two horses for one hour, and 

 sufficient to propel an omnibus through Paris, will be obtained. 

 This use of ammonia is believed, by the projectors, to be feasible, 

 because, first, gaseous ammonia may easily be liquefied ; secondly, 

 its vapour affords at ordinary temperatures a pressure that is 

 utilizable, and it may be superheated without recourse being had to 

 a high temperature ; and, In stly, the latent heat maybe recovered 

 from the utilized vapour, and communicated to the vapour which is 

 about to be produced, by a mere solution of the gas in water. It is 

 proposed to manufacture liquid ammonia in large quantities in a 

 central establishment, from which it will be distributed, as required, 

 to the various omnibuses, etc. ; and to bring to the same establish- 

 ment the water in which the ammoniacal vapour will have been 

 condensed, that the ammonia may be recovered from it. 



