400 ADDITIONAL PHENOMENA OF NATURAL MAGIC. 



the great progress of recent discovery. Photography has 

 given accuracy of detail and life-like intensity to the 

 subjects displayed by the lantern, while improvements in 

 the mechanism, together with lime ball, magnesium, and 

 other powerful means of illumination, have been success- 

 fully applied to produce almost a daylight clearness on 

 the screen compared with the darkness in which the 

 audience sits in viewing such objects. How far Sir David 

 had anticipated some of the most advanced improvements 

 by his suggestions however will appear from the following 

 passage in a recent publication compared with his letter 

 on this subject : 



" An ingenious experimentalist, desirous of showing 

 various chemical phenomena by means of the magic 

 lantern, makes a glass tank, into which different liquids 

 or solutions may be poured, which will illustrate the effect 

 of refraction on light and other phenomena. If a pipette 

 be skilfully used to introduce some of the solutions into 

 the water in the tank, the appearance thrown on the 

 screen is that of a submarine volcano, pouring forth 

 clouds of smoke and torrents of lava, which, however, are 

 soon absorbed in the surrounding ocean. A solution of 

 cochineal in alcohol, similarly introduced, produces the 

 effect of a magnificent crimson fountain : a solution of 

 litmus appears as a delicate blue sky ; a few drops of acid 

 being let fall into this give a variety of forms and com- 

 binations, as of clouds seen in a sunset sky. Black, 

 stormy clouds may be produced by dropping into the 

 water a small quantity of sulphate of copper in solution 

 and weak ammonia ; and with dilute sulphuric acid and 

 ferrocyanide of potassium, other cloud-effects can be repre- 

 sented which have a most impressive appearance on the 

 screen. It is possible also to show the changes in colour 

 produced by chemical reaction, the decomposition of water 

 by a galvanic current, and the convection of heat by 



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