86 On the MOTION 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 fubject, but 

 more efpecially becaufe its difcuflion depends on a more gene- 

 ral, and hitherto unconfidered fubject in phylico-mathematical 

 fcience, the motion of light as affetled by bodies which are alfo in mo- 

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

 necefTary for my elementary courfe of lectures, and I then in- 

 vestigated the fundamental proportion which I fhall include in 

 this difcourfe. Perhaps I fhould offer fome apology for troubling 

 the Society with my thoughts on the fubject before I have put 

 them into a more perfect form. I fhall frankly tell my reafons 

 for this conduct. This paper of Mr Boscovich mufl excite 

 the attention of philofophers. Other fpeculations alfo which 

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

 tion to the fubject, 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 imperfect 

 account of them. 



I shall therefore lay before the Society a fhort account of 

 the experiment, as propofed and defcribed by Mr Boscovich, 

 and of the remit which he expects from it, and fome of the 

 mod 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 (late 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 expects, but eflablifhed if it fhould be what 

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

 rtion for determining the reflection and refraction of light 



by 



