5° 



DESIGN IN NATURE 



PLATE XXXI 



Fig. 1. 



Fl(^ 2. 



Fig. 3. 



Plate xxxi. illustrates lines of force, motion, and light as seen in electric sparks. 



Fig. 1. — Photograph of a typical electric spark by A. Thiirluirn. Shows radiating, branched ap]iearanee presented bv the electrical 

 discharge wlien acting on a highly sensiti^'e photographic plate. 



Fig. 2. — A similar photograph by A. Thurburn, where the electric spark assumes a radiating and still more branched and tree-like 

 appearance. 



Fig. 3. — A somewhat similar photograph by Dr. Adams, where the electric sparks have assumed a radiating, branched and 

 feathery appearance ; Rontgen ray pictures of the hands being seen in the background. Pictures of this class are most conveniently 

 obtained by placing two photographic plates back to back and inserting between them the points of a discharger connected to an 

 induction cnil ; the contact being broken by hand to prevent more than one discharge falling on the plates. Fig. 2 of this plate 

 represents a photograph taken from the plate next the negative terminal ; Fig. 3, that taken from the plate next the positive terminal. 



