Boyal Societij of Edinburgh. 479 



Sciences, Paris. The Right Rev. the Lord Bishop of Norwich, P res 

 L.S., F.G.S., &c. John Prideaux, Esq., Plymouth. Corresponding 

 Members. — Richard Thomas, Esq., Civil Engineer, Mellingye, near 

 Falmouth. Jonathan Couch, Esq., F.L.S., Polperro. Ordinary 

 Members. — W. Beal, Esq., LL.D., &c., Tavistock. Carteret J. W. 

 Ellis, Esq., A.M., Trengwainton. Seymour Tremenheere, Esq., 

 London. Associate. — Captain Thomas Tiddy, Mona Mine, An- 

 glesea. 



Officers and Council for the present year. President. — Davies 

 Gilbert, Esq., D.C.L., V.P.R.S., &c. &c. Vice-Presidents.— idhxi 

 Batten. John D. Gilbert, F.R.S. Thomas Robins. Francis Rodd. 

 Secretary and Curator. — W.J. Henwood, F.G.S., London and Paris. 

 Treasurer. — Joseph Carne, F.R.S., F.G.S., &c. Librarian. — Ri- 

 chard Hocking. Council. — John S. Enys, Assoc. Inst. C.E. Alfred 

 Fox. Samuel Higgs. George D. John. Richard Millett. Samuel 

 Pidwell. John Richards. Rev. Canon Rogers. Benjamin Sampson. 

 James Trembath, Jun. W. Mansel Tweedy, F.H.S. Michael Wil- 

 liams. • 



ROYAL SOCIETY OF EDINBURGH. 



Memorandum on the Intensity of Reflected Light and Heat. By Prof. 

 Forbes*. " At the meeting of the Society on the 4th February, I re- 

 marked, on the occasion of Professor Keliand's paper on the intensity 

 of reflected light, that it was almost without a parallel in science, 

 that a quantitative physical law like that of the intensity of the reflec- 

 tion of light at diflferent angles, should have first been divined by the 

 rare sagacity of Fresnel, and confirmed by the very different but 

 elaborate mathematical investigations which Mr. Green of Cam- 

 bridge and Professor Kelland have applied to the subject, whilst 

 scarcely any attempt has been made towai'ds its verification by di- 

 rect experiment. 



" Some critical cases for polarized light were indeed assumed as 

 the basis of the original formula ; and M. Arago has confirmed it 

 it by one or two intermediate photometrical experiments ; but the 

 chief evidence for the truth of this remarkable law rests on the in- 

 direct observation of the change of the plane of polarization of an 

 incident ray after reflection. 



" It occurred to me, about the end of 1837, that the anomalies of 

 photometrical observations being nearly as unsatisfactory as ever, 

 some light might be thrown upon this important subject by ascer- 

 taining the law in the case of heat, the intensity of which we have 

 no difficulty in measuring. And since the discovery in the case of 

 heat, of refraction, single and double, of polarization, of total re- 

 flection, and the change it produces on polarized light, as well as 

 the change of the plane of polarization by simple reflection, there 

 seems the greatest reason to suppose that the laws of reflection for 

 heat and light, if not identical for both, would be connected by 

 some simple analogy. 



" Accordingly, during the month of December 1837, I made some 

 preliminary observations, which encouraged me to proceed. It ap- 



From the Proceedings of the Royal Society of Edinburgh, March 18, 1839. 



