260 M. Fruunhofer on tlie Laws 



system of lines, consisting of straight parallel lines, atid can 

 therefore be expressed by the same equation. 



NOTES ON THE PRECEDING PAPER BY THE AUTHOR. 



Note A, see page\257. — The same view might perhaps also 

 be applied to the surface of every Jluid. If the smallest particles 

 of which a fluid consists (the atoms) are not infinitely small, and 

 if they have, however small they may be imagined, some magni- 

 tude, the surface cannot be mathematically even, and light can 

 only be irregularly reflected from that surface, according to the 

 principles of interference. There is no occasion to assume, as ap- 

 pHes also to artificial surfaces, that there must be level surfaces 

 again between these unevennesses. Nothing further is required 

 than that the waves of light diverge from every single point, 

 and they must, by their mutual influence, produce that which 

 the equation expresses. This supposition will not be thought 

 hazardous, if we consider that, for instance, from both the 

 knife-like edges of a small aperture, the waves of light must 

 in one sense diverge according to the interference, in order to 

 produce spectra which may be seen through a single aperture, 

 and that the knife-like edges, as experience teaches us, need 

 not to be mathematically true. The colours also of thin lay^ 

 ers^ (the Newtonian coloured rings) may, under the same sup- 

 position that the surfaces consist of minute unevennesses, be 

 deduced from the theory of interference. I have made a num- 

 ber of new experiments respecting these coloured rings, which, 

 however, are not suited to a communication in this short re- 

 port, and must be still further prosecuted. It is not improbable 

 that the ayigle of polarisation of a refracting medium may 

 perhaps give some clue concerning the magnitude of the small- 

 est particles of this matter, as the experiments have shown 

 w is smaller in the refracting media than in vacuo. From this 

 the law of refraction may be very simply deduced, as it has 

 been ere now already explained, according to the system of 

 undulations, since the pulses of the waves of light of a de- 

 termined sort must repeat themselves under all circumstances 

 at equal intervals of time ; but as these waves are smaller in 

 a refracting medium, the light requires in a refracting sub- 

 stance, in the same proportion, more time for its propagation. 

 According to every hypothesis in which the matter is repre- 



