Observations on Monochromatic Light. 14-5 



as to sec through it a prismatic spectrum of the luminous aper- 

 ture. Take another prism equally good, and view through it. 

 any portion of the first spectrum, by refracting that portion 

 towards the violet extremity, and it will be seen that it is perfect- 

 ly unchanged in its nature and colours by the second refraction. 

 The lines will be seen as distinctly as before, and not a vestige 

 of any other colour will be seen but that of the coloured por- 

 tion itself. 



In reference to the perfection of monochromatic vision, the 

 following experiment will be decisive. Place a printed page 

 of a small type upon a table illuminated by the sun. Stand- 

 ing at the distance of some feet, view this page through a 

 prism so that the plane of its refraction is parallel to the lines 

 in which the types are arranged. The print will be entirely 

 illegible, each letter being blurred with a prismatic spectrum 

 of the white spaces between the sides of the types. Let the 

 page be now illuminated by the light transmitted through a 

 leaf of red paper, and the words and letters will be distinctly 

 legible, though still indistinct on account of the red light not 

 being homogeneous. Shut the window shutters, and illumi- 

 nate the page with a monochromatic lamp : The words and 

 letters will now be beautifully sharp and distinct, and except- 

 ing their slight expansion in one direction by refraction, they 

 will be as clearly seen as if they were viewed through a plate 

 of parallel glass, or with the eye alone. 



If Dr Goring will therefore substitute the monochromatic 

 lamp in place of the sun, we have no doubt that he will change 

 his opinion on the subject of monochromatic vision, and if his 

 health will permit him to devote his acute mind, and apply his 

 great practical knowledge to microscopical discovery, we pledge 

 ourselves that he will find monochromatic light the most power- 

 ful instrument of discovery which optical science can at present 

 command. 



In the use of single chromatic microscopes, a great deal may 

 be done to improve the image, and even free it from colours 

 when particular kinds of objects are used. Let it be required, 

 lor example, to determine the place of an object consisting of 

 close parallel lines, in order to obtain the most perfect vision 

 of it by a single chromatic lens. — The lens should, in \\\cjirst 



NEW SKRIES, VOL. V. NO. r. JULY 1831. K 



