86 On the MO TIO N of LIGHT. 



health does not at prefent permit me to give fuch an account of 

 it as its importance deferves. I propofe, however, to undertake 

 it as foon as I am able. This I am incited to do, not merely 

 on account of the Angularity of this particular fubje(5t, but 

 more efpecially becaufe its difcuflion depends on a more gene- 

 ral, and hitherto unconfidered fubjedl in phyfico-mathematical 

 fcience, the molioti of light as affeSled by bodies which are alfo in mo- 

 tion. This I have confidered fome years ago, as far as I thought 

 neceflary for my elementary courfe of letStures, and I then in- 

 vefligated the fundamental propofition which I fhall include in 

 tliis difcourfe. Perhaps I Ihould offer fome apology for troubling 

 the Society with my thoughts on the fubje(fl before I have put 

 them into a more perfed form. I Ihall frankly tell my reafons 

 for this conduct. This paper of Mr BoscovicH muft excite 

 the attention of philofophers. Other fpeculations alfo which 

 have lately been made by ingenious men, will turn the atten- 

 tion to the fubjedl, and enquiries will be inftituted, and their 

 refults made public. I fhould not chufe to be thought indebted 

 to the refearches of others for the refults of my own enquiries, 

 and therefore wifli to afcertain my claim to any thing which 

 may be valuable in my fpeculations, by this prefent imperfedt 

 account of them. 



I SHALL therefore lay before the Society a fliort accoiint of 

 the experiment, as propofed and defcribed by Mr BoscoviCH, 

 and of the refult which he exped^s from it, and fome of the 

 moft remarkable confequences which he deduces from this re- 

 fult. I (hall, in the next place, point out the overfight which 

 he has made in announcing the refult, and ftate what ought to 

 be the refult, on the phyfical principles adopted by him ; prin- 

 ciples which will be overturned if the refult of the experiment 

 fhould be what he expedls, but eflablifhed if it fliould be what 

 I affert. In the lafl place, I fhall give the fundamental propo- 

 fition for determining the reflexion and refradlion of light 



by 



