Page:Popular Science Monthly Volume 92.djvu/694

 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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