134 SOIOPTICON MANUAL. 



about J inch apart. Now coat the copper wires and the 

 wood with melted parafime, but take care that none gets 

 on the platina; this will insulate the copper wires and 

 prevent the wood from absorbing any moisture. This 

 little frame placed in the tank, immersed in acidulated 

 water (water with a few drops of sulphuric acid), and 

 the terminal wires attached to say two cells of Groves' 

 battery, will show the decomposition of water admirably. 

 A similar piece of apparatus with the terminal wires at 

 the centre of the board, united by a vertical coil of very 

 fine platina wire, will be found useful in illustrations of 

 circulation by heat. Such a frame immersed in clear 

 water will be seen on the screen as a black coil, seem- 

 ingly hanging down from a black bar on the top of the 

 screen; if now, by means of a pipette, some colored 

 fluid, say a solution of permanganate of potash in water, 

 be carried to the bottom of the tank, it will on the screen 

 seem to spread itself out as a red stripe under the black 

 one and enveloping the little coil; a current of elec- 

 tricity passed through the wire will heat the little platina 

 coil and thus heat the water in contact with it, so that 

 currents will be established in the fluid, carrying with 

 them the colored fluid in a very beautiful curling cloud 

 of color. 



I mention to you these few examples, of how readily 

 the needful appliances for illustrations can be improvised ; 

 now I have frequently heard persons say that they 

 " feared the expense entailed in the use of a lantern " 

 that "the lantern is so useless without a great many 

 accessories, which are so expensive in themselves." 

 Feeling a lively interest in your very meritorious in- 

 vention, I have volunteered these hints, which I beg you 

 will, if you see fit, use to your benefit. 



Yery truly yours, 



COLEMAN SELLERS. 



