producing and fixing Electrical Figures. 65 



the impression as it does with an ordinary photograph ; and the 

 glass plates being washed with distilled water and dried, showed 

 no impression when breathed on. 



6. An electric impression of the word Volta was well rubbed 

 with a handkerchief, then washed with water and alcohol, then 

 dried ; the impression still came out by breathing upon it. 

 Some one of the chemicals used in the collodion process had 

 probably had the effect of removing the figure in Experiment 5, 

 but T have not yet ascertained to which this removal is due. 



7. Letters cut in tinfoil were substituted for those of paper; 

 the effect was the same, but it seemed to me more feeble. 



8. A solution of nitrate of silver was poured over the surface 

 of an electrized plate, so as to form a bath on its surface ; a rake, 

 formed of ten common pins, was made to touch the glass with 

 its points along the course of the invisible image ; the silver was 

 of course precipitated in an arborescent form, and I thought it 

 probable that the lines of deposition might follow the course of 

 the invisible image, but I could not be certain of any such effect, 

 though in one experiment there seemed to be some slight indi- 

 cation of it. 



The above experiments were repeated many times, both with 

 positive and negative electricity from the coil. At first I be- 

 lieved I had found a remarkable difference in the effect of the 

 change of direction of the discharge in the cases where hydrofluoric 

 acid was employed ; and in two experiments, in which the tinfoil 

 of the upper glass plate was connected with the positive terminal, 

 the impression of the word on the lower side of the upper plate 

 after exposure to the vapour, was polished, while the residue of 

 the plate was frosted ; and in two subsequent cases, the upper 

 tinfoil being connected with the negative terminal, the reverse 

 was the case. In subsequent experiments, however, great irre- 

 gularities took place in this relation, and it seemed to depend 

 on the time of exposure and on slight differences in the distance 

 between the paper letters and the glass, the latter not being 

 broughtintoperfectlyuniform contact with thesurfaces of the glass. 



After the first few experiments I placed a marble paper-weight 

 on the upper glass, and found the effects more uniform and perfect. 



An electrization for periods of from five to ten minutes, pro- 

 duced the sharpest and clearest effects ; when the electrization 

 was prolonged, a blur or second margin gradually appeared, and 

 increased in extent around the outline of the letters, having 

 somewhat the appearance which would have been presented had 

 the paper letters been moist, and the liquid slightly extended 

 itself from their edges over the glass. 



When the electrization was thus prolonged, the figures were 

 visible on inclining the glass to the light, without breathing on 

 them, and gave a strong impression of the glass having suffered 



Phil, Mag. S. 4. Vol. 13. No. 83. Jan. 1857. F 



