Royal Society. 453 



but that it is applicable to any eyepiece positive or negative to the 

 erecting eyepiece, and, indeed, to any telescope of fluid or glass, and 

 also to refractors. 



A paper was also read, entitled, " Some remarks in reply to Dr. 

 Daubeny's Note on the Air disengaged from the Sea over the site of 

 the recent Volcano in the Mediterranean." By John Davy, M.D., 

 F.R.S. Assistant Inspector of Army Hospitals. 



Respecting the air in question, which Dr. Davy had found to con- 

 sist of about 80 per cent, of azote and 10 oxygen, he had remarked 

 that two views might be taken of its origin ; the one, that it was of 

 volcanic source ; the other, that it was derived from the sea water, 

 and merely disengaged by the heat of the volcano. Dr. Davy, reject- 

 ing the former of these views, had adopted the latter, for reasons, the 

 validity of which was controverted by Dr. Daubeny* j and the purpose 

 of the present paper is to answer the objections urged against them, 

 and to bring additional evidence in support of his opinion. 



A paper was then read, entitled, "On the number of Primitive 

 Colorific Rays into which White Light may be separated." By Paul 

 Cooper, Esq. Communicated by J. G. Children, Esq. Sec. R.S. 



From a consideration of the circumstances in which white light is 

 decomposed by the prism, in different experiments, and of the various 

 appearances of the spectra which result, the author is led to the 

 opinion that the primary colours composing white light are not 

 seven, as conceived by Newton j nor four, as supposed by Wollas- 

 ton j but only three: and that these three are not red, yellow, and 

 blue, as imagined by Brewster, but red, green, and violet; the 

 first and last forming the terminal parts of the spectrum, and the 

 green occupying an intermediate position ; and the various tints 

 which intervene being the result of superpositions, in various quan- 

 tities, of these respective primary colours. He pursues the conse- 

 quences of this hypothesis, applying it to a great variety of forms of 

 experiment, not only by the direct observation of beams of refracted 

 light, but by viewing the prismatic spectrum through different media, 

 capable of absorbing each of the primitive colours in different degrees : 

 and he finds the results to accord exactly with the hypothesis he pro- 

 poses, and on which he therefore concludes that their true explanation 

 must be founded. He conceives that the errors of preceding experi- 

 mentalists have arisen from their neglecting to take into account the 

 effects of diffraction, which introduces considerable confusion into the 

 results. 



A paper was also read, entitled, •* An Investigation of the Laws 

 which govern the Motion of Steam- Vessels, deduced from expe- 

 riment." By P. W. Barlow, Esq. Civil Engineer. Communicated 

 by Dr. Roget, Sec. R.S. 



The author commences with the description of a paddle-wheel for 

 steam-vessels, of a new construction, in which the floats are made to 

 enter and leave the water nearly in a vertical position. He then inves- 

 tigates several formulae adapted to the calculation of the forces and 



* An abstract of Dr. Daubeny's note was given in vol. iii. p. 447. 



