80 LETTERS ON NATURAL MAGIC. 



saline substances, soluble in water, are laid at the 

 bottom of the trough, the density will diminish 

 upwards, and the figure will undergo the most 

 curious elongations and contractions. Analogous 

 effects may be produced by the application of 

 heat to the surface or sides of the trough, so that 

 we may effect at the same time both an increase 

 and a diminution in the density of the water, in 

 consequence of which the magnified images will 

 undergo the most remarkable transformations. 

 It is not necessary to place the glass plate which 

 contains the figure within the trough. It may be 

 placed in front of it, and by thus creating as it 

 were an atmosphere with local variations of 

 density, we may exhibit the phenomena of the 

 mirage and of looming, in which the inverted 

 images of ships and other objects are seen in the 

 air, as described in another letter. 



The power of the magic lantern has been 

 greatly extended by placing it on one side of the 

 transparent screen of taffeta which receives the 

 images, while the spectators are placed on the 

 other side, and by making every part of the glass 

 sliders opaque, excepting the part which forms 

 the figures. Hence all the figures appear lumi- 

 nous on a black ground, and produce a much 

 greater effect with the same degree of illumina- 

 tion. An exhibition depending on these principles 

 was brought out by M. Philipstall in 1 802, under 

 the name of the Phantasmagoria, and when it 

 was shown in London and Edinburgh, it pro- 

 duced the most impressive effects upon the spec- 

 tators. The small theatre of exhibition was 

 lighted only by one hanging lamp, the flame of 

 which was drawn up into an opaque chimney or 



