2; 8 HOW TO WORK 



object of this arrangement is to collect and concentrate the 

 light emitted by a cylinder of lime rendered incandescent by an 

 ignited jet of oxy-hydrogen gas, upon the surface of the photograph, 

 through which it passes, and then converges upon an achromatic 

 combination placed at a proper focal distance in front. * The rays on 

 passing onwards diverge, and the enlarged shadow of the photograph 

 is projected upon an opaque or transparent screen. By this means 

 all the details of an object less than a pin's point in size may be 

 shown with perfect definition, twenty feet in diameter. The hydrogea 

 may be obtained from any house gas-supply by simply connecting the 

 tap of a gas bracket by a piece of flexible tubing with the hydrogen 

 tube of the jet. The oxygen is obtained by heating a mixture of 

 chlorate of potash and oxide of manganese in a proper retort, and 

 collecting the gas in a wedge-shaped gas-bag, after passing it through 

 a washing bottle to purify it. The stopcock of the gas-bag is con- 

 nected with the oxygen tube of the jet by flexible tubing. The jet 

 is so arranged that it is impossible for any accident to occur in the 

 shape of an explosion, the gases only being combined at the 

 extremity of the jet. When house gas is not attainable the jet of 

 oxygen may be forced through a spirit flame on to the lime ball, or 

 if a small disc of seven feet in diameter is considered sufficient, 

 such photographs may be shown by means of a paraffine or other 

 hydro-carbon lamp, if the triple condenser and single achromatic 

 lens recently introduced by Mr. Highley be employed. 



The most intense light is obtained by replacing the house-gas 

 (carburetted hydrogen), with pure hydrogen and burning both gases 

 under an increased pressure, and mixed in a suitable jet, just before 

 being forced upon the lime ball. 



Mr. Robert Grant, of New York, has remedied the inconvenience 

 of the usual India-rubber gas-bags by constructing cylinders of iron 

 of about one cubic foot capacity, and charging these by means of 

 condensing pumps with the gas to the pressure of 30 atmospheres, 

 being equivalent in contents to six of the gas-bags generally 

 employed. The advantages over the gas-bags are, that these 

 reservoirs are cheaper, last longer, and keep the gases any length 

 of time undeteriorated. They are always ready for use, the 

 cumbrous pressure boards and weights are dispensed with, and they 

 are free from danger if purchased from a maker that can be relied 

 on. Every bottle should be subjected to a suitable test before 

 it is sent out. The drawback to this arrangement is that the 



* Mr. Highley makes a combination of three lenses 3-^ inches in diameter into 

 a condenser. 



