26 Dr. Tyndall on the Progress of the Physical Sciences : 



they are facts ; and facts, too, which in my opinion will, if once 

 better understood than they are now, throw floods of light upon 

 the thick darkness with which the chemical world is as yet 

 covered. And I am inclined to think so, because it is very 

 likely that the so called catalytical phfenomena reveal the very 

 clementai-y, and on that account the most important, actions or 

 functions of matter. 



I am, my dear Faraday, 



Yours most truly, 

 BAle, May 1, 1851. C. P. Schcenbein. 



IV. Reports on the Progress of the Physical Sciences. 

 By John Tyndall, Ph.D., Marburg. 



1. The Reversion-prism, and its application as oculaf to the Terrestrial 



or Day-Telescope, by H. W. Dove. 



2. Description of several Prism-stereoscopes, and of a simple Mirror^ 



stereoscope, by H. W. Dove. 



3. On the deportment of Crystalline bodies between the electric poles, by 



II. Knoblauch. 



FOR the manuscript of the first two papers I am indebted to 

 the kindness of Professor Dove. The reversion-prism will 

 probably come into practical use both in England and Germany. 

 In leveling instruments, for example, the inconvenience of the 

 common telescope led to Gravatt^s invention of the dumpy-level ; 

 but the inversion of the figures upon the leveling- staves consti- 

 tutes an objection in the eyes of many. M. Dove's invention 

 removes this objection; the reversion-prism sets the figures 

 again erect without rendering a lengthening of the instrument 

 necessary. The application of the invention will render the day- 

 telescope in genei-al a more convenient instrument. 



The stereoscopic apparatus and phsenomena described in the 

 second paper are strikingly simple and beautiful. I would 

 recommend the reader to furnish himself with a pair of prisms 

 and a few stereoscopic drawings ; with their aid the paper will 

 be much more intelligible. 



The paper by Professor Knoblauch has also been handed to 

 me in manuscript. It is highly interesting to observe the par- 

 allelism between electricity and magnetism in the production 

 of phsenomena. The author has demonstrated the action of 

 electricity on crystalline substances in a very convincing manner, 

 and seems to have succeeded in tracing the phsenomena-to the 

 same cause as that to which magneto-optic action has been 

 referred by him and the writer, namely, to peculiarity of aggre- 

 gation. In the ' Report ' the translation of the manuscript is 

 slightly abbreviated. 



