PHYSICAL EXPERIMENTS. 53 



focus or longer, will answer. It is the interior of the 

 ice that is to be projected, and as there is a multitude 

 of planes within it, each one being slowly decomposed, 

 the light will suffer refraction, and one must not look 

 for such plain figures to cover the screen as is repre- 

 sented in Tyndall's work, and in Deschanel's Physics. 

 The forms can be picked out here and there. 



If a lantern be used to project these crystalline forms, 

 remember that the best effect will be obtained with a 

 beam of parallel rays, which, in most lanterns, will 

 necessitate the removal of the front lens of the con- 

 denser.. 



THE LEAD TREE. 



Fill the small glass tank for the solar microscope 

 with a rather dilute solution of the acetate of lead ; ad- 

 just it as for the exhibition of animalcules, using a 

 small lens with a short focus, not more than an inch, if 

 such an one is possessed. Into the solution now drop 

 a very narrow strip of sheet zinc, not bigger than a 

 common sewing-needle ; such a piece can be easily 

 enough cut from a sheet of zinc with a pair of shears. 

 This will at once have a deposit of lead upon it in a 

 beautiful fern structure, which, while you look upon it, 

 grows to be a forest. The same effect can be produced 

 in the larger tank, described farther on, with a smaller 

 magnifying power, by using a small battery of two 

 Grove's cells, and having fine platinum wires to dip into 

 the solution of lead. The lead will be deposited in the 

 fern-form upon one of the wires. After there is a 

 growth of the crystals upon a wire, attach the other end 

 of the wire to the other pole of the battery, and then, 

 completing the circuit again, the lead will be dissolved 

 from the first, and be deposited upon the second. 



