396 OPTICAL PROJECTION 



boiling water, and left to get cold. The cake is supported 

 horizontally in the field of the lantern, and a cold bullet laid 

 on its centre is focussed on the screen and then removed. 

 The three bullets to be used are heated in boiling water long 

 enough to be certain they have all acquired the temperature 

 of 212 F. The leaden one is then taken out first by its 

 handle, and after shaking off the water, gently placed on the 

 centre of the wax ; then the tin one similarly laid about 1^ 

 inches from it on one side ; and lastly the iron or zinc one 

 the same distance on the other side all appearing on the 

 screen. Though much heaviest, the leaden bullet will scarcely 

 sink at all into the wax ; while if the softness and thickness 

 of the plate are well calculated, the tin ball will sink much 

 deeper, and the iron or zinc one will make its way entirely 

 through, and drop into some vessel placed to receive it. The 

 softness of the wax is to be adjusted, according to the exact 

 size of the balls and thickness of the cake, to secure this 

 result. 



230. Spheroidal State. A very shallow silver dish about 

 three inches diameter is supported with its convex side upper- 

 most over an annular Bunsen burner in the field of the lantern, 

 and the burner adjusted to bring the surface to a dull red 

 heat. Taking up in a small sponge some water as hot as the 

 hand will bear, and squeezing out drops to fall upon the hot 

 dish, the rebounding of the drops, like peas, will be clearly 

 projected. 



Reversing the dish to its usual position, and placing the 

 whole lower, and more in front, the beam may be slightly 

 converged from the condensers and reflected down upon it, 

 and a focussing lens adjusted to focus the object upon the 

 ceiling, or a small overhead screen, at a similar angle. The 

 dish being heated as before, nearly boiling water is dropped 

 into it by degrees from a syringe or pipette, till a fluid 

 drachm or more has collected. The water will become a 

 flattened globule, in ceaseless motion, the edges especially 



