s 6 GEOEGB E. PEOWSE ON A NEW 



lens system for enlarging, projecting and focussing the image of the object as illuminated 

 by rays of light passing through a condenser. These parts are all comprised in a small 

 case of wood and metal, in which is placed a four-inch condenser— this size being ample 

 to cover the aperture of an ordinary lantern slide three inches square. The back case of 

 the lantern is provided with a sliding adjustment to establish the proper focal relations 

 between the lens and the condenser. The spindle upon which the lime is placed is also 

 provided with the usual means for transverse and vertical adjustment and adjustment of 

 the jet relatively to the lime. An important feature consists of means for vertical adjust- 

 ment of the entire instrument This is effected by having the body hung on pivots at 

 the summit of two metal triangles. From each pivot there depends an arm carrying at 

 its lower extremity a clamp operated by a thumb screw. This latter passes through and 

 engages upon a short arc opening in each triangle in such a way that the body of the 

 lantern may be adjusted horizontally, or vertically above and below this position within 

 an extreme range of about 30", the position desired being firmly secured by the clamping 

 action of the thumb screws. 



The generator consists of an iron or steel tube with a semi-circular cross-section. 

 Into the flat or lower side are inserted a number of copper cups, each of a capacity to con- 

 tain sufficient mixture to maintain the light for about fifteen minutes. The different 

 rates of conduction in the two metals of the retort serve two purposes. The copper being 

 a rapid conductor, brings about a speedy fusion of the chlorate of potash, which quickly 

 o-ives off gas. The iron, by its slower conductivity, serves to retard the transmission of 

 heat from cup to cup, thereby prevents action taking place in any cup not directly heated, 

 and secures complete control of the whole operation. Each cup is heated in turn by 

 means of a spirit lamp or a small Bunsen burner, as may be desired, the transfer of heat 

 from one to the other being effected automatically by an attachment which is operated 

 by the receiver w^hen the gas has reached a certain degree of exhaustion. 



The washer, saturator and regulator are combined in one piece, measuring Y.S x 12.5 

 x 30.5 cm. This is placed directly beneath the body of the lantern between the triangular 

 supports. The central longitudinal section is occupied by the washer. This consists of 

 a tube arranged with fine wire cloth, and filled with a moist filtering substance, which 

 serves to arrest any particles of carbon or other similar impurities which may pass over 

 from the retort. On each side of the washer is a similar tube filled with pine-wood saw- 

 dust, which is charged with sulphuric or petrolic ether, as may be desired. The form 

 of saturator is an improvement upon that usually employed, while the construction is 

 such as to avoid all possibility of explosion. Towards one end, and directly over the 

 washer, is a small standpipe with two stopcocks and a regulator. The latter consisls of 

 a rubber diaphragm, upon which rests a lead disc weighing about 136 grammes. The 

 amount of gas passing through from the regulator to the burner is determined by the 

 adjustment of two needle-point valves, one for each gas, and thus the production of a 

 brilliant light is readily secured 



The gas receiver is contained in the case which holds the entire instrument when in 

 transport. It consists of a rubber bag, having a capacity of nearly one foot, the upper 

 part of which is formed of a tin pan working upon two upright metal posts, one of which 

 serves as a tube for the conveyance of gas to and from the receiver. Into the pan there 

 is loosely fitted a second pan, designed to be filled with water in order to establish the 



