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of bodies influenced by magnetic, electric, or chemical action. 
More recent observations had induced him to alter this 
opinion. He thought the phenomena were caused by inter- 
ference of light accompanied by diffraction fringes of colour 
produced by the projection of a dark body against a bright 
sky. The actinic effect of these fringes might possibly be 
increased or decreased according to the amount of chromatic 
correction of the camera lens for the primary and secondary 
spectra. Mr. Dancer stated he had frequently noticed the 
reversed action of light from over exposure ; with the old 
Daguerreotype process he had obtained very perfect negative 
instead of positive pictures. On one occasion, in 1840, he 
accidentally exposed an iodized Daguerreotype plate in the 
camera much longer than the usual time ; in this picture 
the natural colours of the objects were brought out in a 
marked degree. This picture he exhibited to many friends, 
but from not being fixed it faded after some time. Subse- 
quent attempts on the same objects failed in obtaining the 
natural colours. 
