41 6 The Causes, Laws, and Phctnomena of Heat, Gases, S^c, [Ju N e, 



ciatiiig" those elements in Uie particular manner that nature has 

 adopted. I might hkewise unfold the cause of the opacity and 

 transparency of bodies, and show that the phcenomena of reflec- 

 tion and refraction consist in two distinct forces residing the 

 one without the other, and acting upon the luminous particles 

 separately and distinctly near the surfaces of bodies ; that the 

 figures of the molecules of light are the cause of the fits of easy" 

 reflection and transmission ; of the pha^nomena of polarization ; 

 and combined with the figure of the nitegrant particles of doubly 

 refracting crystals, likewise the cause of double refraction and 

 its consequent phajnomena. And by the same principles I 

 might show how to explain the disproportional dispersion of- 

 light, and the various phisnomena of diifVaction, as well as the 

 intersectionary bands lately discovered by Mr. Knox, and some 

 circular and hyperbolic bands discovered by myself.* I might 

 also, from our solution of the problem of gravitation, demonstrate, 

 that the particles of light, however different in size, must be 

 emitted with nearly equal velocities; that the velocity of the 

 solar and astral light, conformably to phgpnomena, should be 

 nearly equal ; and that it is to the reciprocal action of the sun 

 and stars, that gravitation itself, and consequently all the other 

 phaenomena, are owing ; but as I have considerably extended 

 this memoir beyond the hmits I at first intended, and as my 

 ideas on some of these subjects are not yet sufficiently matured, 

 I have deemed it better to reserve what I may have further to 

 say to a future period, when I may be enabled to put these and 

 some other things together in a more methodical form. 



For like reasons, 1 shall not now stop to inquire, whether the 

 phenomena of magnetism, electricity, and galvanism, are refera- 

 ble to the same prmciples or not. Nor shall I attempt to make 

 any observations on the still more metaphysical properties 

 ascribed by Newton to our gravific medium ; namely, whether 

 ** Sensatio omnis excitatur; et membra animalium ad volunta- 

 tem moventur, vibrationibus hujus spiritus, persolida nervorum' 

 capillamenta, ab externis sensuum organis ad cerebrum, et u 

 cerebro in musculos, propagatis ; " for these are speculations 

 much too metaphysical for this place, and are besides things 

 ** quae paucis exponi non possunt." 



I am, dear Sir, your obedient humble servant, 



Brtttol, Knoivknm,f Mai/23, 1820. JoHN HeRAPATH. 



• It was intended to make the substance of tins communication a supplement to one 

 containing an account of these bands, with a mathematical explication of their cause ; 

 but finding that I could not explain myself in so few woids as I expected, I have thought 

 it preferable to omit the optical part altogether. 



f This was written at Knowle Hill, but the author now resides at Cranford, Houn^ 

 Blow, London. 



