Intelligence a?id Miscellaneous Articles. 



65 



to have been obtained, including several very 2»/pro6«t/e alternatives, 

 for tlie purpose of showing the necessity that exists for the repetition 

 of the experiment, with the precautions suggested in these remarks, 

 before any important conclusions can be founded upon it respecting 

 the theory of galvanism. 



Dec. 28, 1829. E. W. B. 



EXPEKIMENTS ON LIGHT AND SHADOW MADE BY MEANS OF 

 THE PRISM. BY DR. J. READE. 



Exp. 1. — Having placed a piece of white paper close to one of 

 the planes of an equilateral prism, on looking through it at the 

 clouds the black angles of the prism reflecting their shadows were 

 very apparent, as represented in the following figure : 



A B, a sheet of white paper held close to and touching the plane 

 of the prism a c. ab c three opake and 



dark angles forming black shadows, which q 



passing through the plane fall on the pa- ...-■;/ s 



per A B. If we now hold a lighted can- 

 dle behind the prism, these black shadows 

 are immediately changed to blue at top, 

 orange at the bottom, demonstrating in 

 the most conclusive manner, that it is tlie 

 black shadows of the prismatic angles 

 which give the colours of the spectrum, 

 and not any decomposition of the solar 

 ray. If when the sun is shining we bring 



the prism with its attached paper into the rays, and then turn the 

 instrument on its axis so as to bring the plane a c to an angle of 

 io", with the paper A B, as thus represented, a reflected and not 

 a refracted spectrum is formed. The black shadows from the an- 

 gles a and c are passed through the 

 j)rism and rarefied by the reflected 

 light from the plane Oc into orange 

 at the bottom, blue at the top. On 

 looking at the inside of the plane 

 b c, we see the window reflected 

 as soon as the coloured spectrum 

 is formed; and, as I believe Mr. 

 Brougham first remarked, if a pin 



or any other slender body be held in the spectrum, light-coloured 

 shadows are seen. Now as every separate liglit forms its own sha- 

 dow, we need no stronger proof that light is reflected from the 

 plane ic; and as the light is reflected upwards, the spectrum 



ascends on the opposite wall. t t> ht t-k 



' ' J. Reade, M. D. 



P.S. Since writing tlie above, I have made the following experi- 

 ment : The sun shining on the slates of an opposite roof to my bed- 

 chamber, I pulled down the blinds, leaving a triangular corner open, 

 I now held a pencil before a sheet of white paper and saw three 



N. S. \'oI. 7. No. 37. Jan. 1830. K coloured 



