MAGIC LANTEKN. 79 



magnified 50 or 100 times ; and when we consider 

 what kind of artists are employed in their execu- 

 tion, we need not wonder that this optical instru- 

 ment has degenerated into a mere toy for the 

 amusement of the young. Unless for public ex- 

 hibition, the expense of exceedingly minute and 

 spirited drawings could not be afforded ; but I 

 have no doubt that if such drawings were exe- 

 cuted, a great part of the expense might be saved 

 by engraving them on wood, and transferring 

 their outline to the glass siders. 



A series of curious representations might be 

 effected, by inserting glass plates containing suit- 

 able figures in a trough having two of its sides 

 parallel, and made of plate glass. The trough 

 must be introduced at EF, so that the figure on 

 the glass is at the proper distance from the object 

 lens D. When the trough is filled with water, 

 or with any transparent fluid, the picture at PQ 

 will be seen with the same distinctness as if the 

 figure had been introduced by itself into the 

 groove EF ; but if any transparent fluid of a 

 different density from water is mixed with it, so 

 as to combine with it quickly or slowly, the ap- 

 pearance of the figure displayed at PQ will 

 undergo singular changes. If spirits of wine, 

 or any ardent spirit, are mixed with the water, 

 so as to produce throughout its mass partial 

 variations of density, the figure at PQ. will be as 

 it were broken down into a thousand parts, and 

 will recover its continuity and distinctness when 

 the two fluids have combined. If a fluid of less 

 density than water is laid gently upon the water, 

 so as to mix with it gradually, and produce a 

 regular diminution of density downwards 'Or if 



