Making Animals Transparent 



We used, as children, to read about invisi- 

 ble cloaks. Read how a rat got his " cloak" 



HG. WELLS once wrote a striking 

 story about an invisible man, who 

 owed his invisibility to the fact 

 that a method had been discovered of 

 rendering the refractive index of his 

 body to light exactly the same as that of 

 the atmosphere. In other words, his 

 body became absolutely transparent and 

 hence invisible. 



Perhaps the principle may be better 

 understood if we consider the case of a 

 glass tube. Ordinarily the tube reflects 

 lights and objects. Placed in water, the 

 tube becomes much more transparent; 

 but placed in a liquid having the same 

 'index of refraction as the material of the 

 glass, the tube is hardly visible at all. 

 On the other hand, "ground glass" 

 is opaque because the rays of light 

 are bent ; the surface of the glass is so 

 broken up that the separate rays of 

 light do not pass through in a direct 

 line at all. 



That Wells was not merely romancing is 

 strikingly demonstrated by the accom- 

 panying photographs 



which were made for the POPULAR 

 Science Monthly with the consent of 

 Doctor Harmer of the British Museum. 

 The trustees of the Museum applied to the 

 proper British authorities for permission to 

 use the discovery disclosed in a German 

 patent granted to Hermann Streller of 

 Leipsic. Streller actually patented what 

 appears to be a valuable process "for 

 rendering organic and inorganic bodies 

 transparent and translucent" by juggling 

 the refraction of light in the way pro- 

 posed by H. G. Wells in his story. 



The rat that Doctor Harmer treated 

 passed through more than one solution 

 'before he was reduced to comparative 

 transparency. First of all the rat was 

 stripped of his fur overcoat. Reduced 

 to stark nakedness, he passed through 

 solution after solution. Like all other 

 animals, a rat consists largely of water. 

 This was removed and he was immersed 

 in weak alcohol. Gradually the alcohol 

 was strengthened until the water was all 

 expelled, and the rat was practically 

 pure alcohol. Then a fluid was intro- 



This rat has been rendered partially invisi- 

 ble by the chemical treatment of his body 



Here are three objects — opaque, semi-trans- 

 parent, and transparent. Note the rat's bones 



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