2 ?6 PLEASANT WAYS IV SCIENCE. 



the paper to the negative pole produces a blue mark on the 

 chemically prepared paper.* 



We see that by Bain's arrangement a paper is marked 

 with dots and lines, corresponding to round and elongated 

 holes, in a ribbon of paper. It is only a step from this to 

 the production of facsimiles of writings or drawings. 



Suppose a sheet of paper so prepared as to be a con- 

 ductor of electricity, and that a message is written on the 

 paper with some non-conducting substance for ink. If that 

 sheet were passed between the knobs at a (the handle H 

 being pressed down by a spring), whilst simultaneously a 

 sheet of Bain's chemically prepared paper were passed 

 athwart the steel pointer at the receiving station, there 

 would be traced across the last-named paper a blue line, 

 which would be broken at parts corresponding to those on 

 the other paper where the non-conducting ink interrupted 

 the current. Suppose the process repeated, each paper 

 being slightly shifted so that the line traced across either 

 would be parallel and very close to the former, but precisely 

 corresponding as respects the position of its length. Then 

 this line, also, on the recording paper will be broken at 

 parts corresponding to those in which the line across the 

 transmitting paper meets the writing. If line after line be 

 drawn in this way till the entire breadth of the trans- 

 mitting paper has been crossed by close parallel lines, the 

 entire breadth of the receiving paper will be covered by 

 closely marked blue lines except where the writing has 

 broken the contact. Thus a negative facsimile of the 

 writing will be found in the manner indicated in Figs. 8 

 and 9-t In reality, in processes of this kind, the papers 

 (unlike the ribbons on Bain's telegraph) are not carried 

 across in the way I have imagined, but are swept by 



* The paper is soaked in dilute ferrocyanide of potassium, and the 

 passage of the current forms a Prussian blue. 



t Sir W. Thomson states, in his altogether excellent article on the 

 electric telegraph, in Nichol's Cyclopadia, that the invention of this 

 process is due to Mr. Bakewell. 



