36 OPTICAL PROJECTION 



power of a reflector entirely depends upon this, and upon the 

 reflector taking up enough rays to illuminate to the edge of 

 the condenser. 



To get a good light, the glass chimney and the reflector 

 (best of silvered glass) must be polished bright. A rather 

 loose or woolly wick must be used (the hard wicks used in 

 petroleum Argands will not answer for fatty oil), and, if new, 

 carefully dried before a hot fire, or in the oven, before use. 

 Several hours must be allowed for the oil to soak up in a new 

 wick, and always the lamp is better for warming before the 

 fire, previous to use. Lastly, after trimming anew wick, light 

 the lamp and let it burn several minutes ; then blow it out. 

 It can now be trimmed really clean and smooth, as it could 

 not be before. When finally lit, let it burn a minute or so 

 moderately, and then turn up as high as possible without 

 smoking. 



20. Petroleum Oil Lamps. Paraffin or petroleum oil 

 could be, and was, burnt in some of the preceding lamps, but 

 there was little gained by it, and the first real advance in 

 illumination was made by Mr. L. Marcy, of Philadelphia, in 

 the lamp (and lantern) introduced into England by Mr. 

 Woodbury under the name of the Sciopticon. In this lamp 

 two flat wicks, about two inches wide, were placed with their 

 edges towards the condenser, outer flat cone-pieces directing 

 the air upon the flames, and driving them very close together. 

 The heat of each flame intensifies its neighbour, and the result 

 is a very brilliant light, very ' solid ' also, owing to the depth 

 of wick behind it. The Sciopticon two-wick lamp was found 

 equal to 60 or even 70 candles, and gave a really good disc of 

 9 feet with photographic slides. Its chief fault is, that the 

 space between the wicks generally manifests itself as a rather 

 darker streak up the centre of the screen. 



Partly to avoid this, and partly to get more light, a third 

 wick was soon suggested. This was stated by Mr. Marcy to 

 be inferior to the double wick ; but general experience has not 



