144 Observations on Monochromatic Light. 



Gorino-'s experiments were made with monochromatic light 

 such as his prism could give him, while mine were made with 

 the infinitely superior illumination of the yellow light of a mo- 

 nochromatic lamp, I might have satisfied myself with the reply, 

 that the results which he obtained with the one could not pos- 

 sibly invalidate those which I obtained with the other ; but 

 this would have been a virtual evasion of the difficulty, for I 

 am convinced that monochromatic light properly obtained by 

 the prism is as well fitted for microscopic vision as that of a 

 monochromatic lamp, provided we use a portion of the pris- 

 matic spectrum that has the same limited range of refrangibi- 

 lity. This, however, is almost impossible, and hence the great 

 superiority of artificial yellow light is undeniable. 



The conclusion at which Dr Goring arrives is, that white 

 liobt is as good for microscopical vision as the monochromatic 

 lio-ht which he obtained from the prism, — that such light is 

 not monochromatic, — and that a monochromatic light is still a 

 desideratum. The proof which he gives of these conclusions 

 is this : When any of the prismatic colours were employed to 

 illuminate the microscopic object, the object was fringed with 

 prismatic colours. Of the accuracy of this observation we 

 cannot doubt ; but it is manifest that the prismatic colours 

 employed were compound, and were either formed by an im- 

 perfect prism, or mixed with extraneous light. Instead of 

 suspecting the goodness of his prism, or his method of observa- 

 tion, Dr Goring is led to infer that a certain quantity of white 

 lio-ht enters into the constitution ()f each of the seven coloured 

 rays, and may be rendered manifest by the dispersive powers of 

 prisms and lenses. — This result is in direct opposition to all Sir 

 Isaac Newton's experiments with the prism ; and if Dr Goring 

 will employ the methods suggested by Sir Isaac for obtaining 

 homogeneous light, he will discover the origin of his mistake. 

 As this, however, would be attended with some trouble, we 

 be" to suggest the following experiment which we have made 

 fifty times with the same result. Take an excellent prism, 

 capable of showing Fraunhofer's lines in the spectrum, and 

 having admitted the sun's light through ths narrowest practi- 

 cable opening between the edges of the window shutters, fix 

 the prism vertically at the distance of twelve or fifteen feet, so 



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