PHYSICAL EXPERIMENTS. 55 



projected it is inverted, and as the arborescent deposit 

 hangs upon the wire, it will appear upright upon the 

 screen, and so have a closer semblance to a rapid veg- 

 etable growth. 



A neutral solution of the terchloride of gold will give 

 a characteristic growth upon a piece of zinc, but the 

 solution should be quite weak. 



Salts of copper will give nodular forms upon zinc, if 

 very dilute, and a dense fringe of black copper, if the 

 solution be very strong, sometimes terminating in quite 

 large crystals. 



GRAVITATION. 



Make a frame like the picture, consisting of two up- 

 right posts, about one foot long and one inch square, 

 grooved like flooring on one 

 side of each. Fix these into 

 a board (a) about eight inches 

 by twelve, for a support. 

 Fasten a strip across the top 

 to hold them steady. They 

 should stand about five inches 

 apart. The flange should be 

 cut away from the right-hand 

 standard, from the top down 

 about five inches, so that the 

 weight , which has a tongue 

 on each end, can be put into 

 its place and be free to move 

 up and down between the 

 Fig. 35. standards. A plate of glass 



(c) of proper width must fit in the top, and be fastened 

 by a button (d), or otherwise, and held firmly in place. 

 Procure a pocket tuning-fork, either an A or a C, and 



