Mr. W. B. Croft on Breath Figures. 183 



the dark, but did not get any result on developing : my im- 

 perfect skill in photographic matters leaves this experiment 

 inconclusive. 



Probably all polished surfaces may be similarly affected : a 

 plate of quartz gives the most perfect images, which retain 

 their freshness longer than those on glass. 



Mica and gelatine give poorer results : it is not possible to 

 polish the surface to the necessary point without scratching it. 



On metal surfaces fairly good impressions can be produced 

 if, as Karsten advises, oiled paper is put between the coin and 

 the surface. 



In the order of original discovery the figures noticed by 

 Peter Eiess should come first. He discusses a breath-track 

 made on glass by a feeble electrical discharge ; as well as two 

 permanent marks, noticed by Ettrick, which betray a disin- 

 tegration of the surface. 



I have found that when a stronger discharge is employed 

 more complex phenomena of a similar kind are produced. A 

 6-inch Wimshurst machine is arranged with extra condensers, 

 as if to pierce a piece of glass. If this is about 4 inches 

 square the spark will generally go round it. For a day, 

 more or less, there is only a bleared watery track, -^ inch 

 wide, when the glass is breathed upon ; but after this time 

 others develop themselves within the first, a fine central 

 black line with two white and two black on either side, the 

 total breadth being the original j 3 ^ inch. These breath-lines 

 do not precisely coincide in position with the permanent scars, 

 but the central one is almost the same as a permanent mark, 

 which the microscope shows to be the surface of glass frac- 

 tured into small squares of considerable regularity : on either 

 side is a grey-blue line always visible, which Riess ascribes 

 to the separation of the potash. After several months I found 

 two blue lines on either side, which I believe were not visible 

 at first. Of course these blue lines may be seen on most 

 Leyden jars, where they have discharged themselves across 

 the glass. 



In ]842 Moser, of Konigsberg, produced figures on 

 polished surfaces by placing bodies with unequal surfaces 

 near to them : the action was ascribed to the power of light, 

 and his results were compared with those of Daguerre. 

 Moser says, "We cannot therefore doubt that light acts 

 uniformly on all bodies, and that, moreover, all bodies will 

 depict themselves on others, and it only depends on extrane- 

 ous circumstances whether or not the images become visible. " 

 In general, the multitude of images would make confusion ; 

 it can only be freshly polished surfaces that are free to reveal 



