VOL. LX."] PHILOSOPHICAL TRANSACTIONS. 65 



them, so as to see their shape more distinctly. The two masses of bones are 

 blended with pieces of the marble, of which the whole rock of Gibraltar, as I 

 am informed, is composed; and all the constituent pieces are cemented strongly 

 together with a brownish coloured calcareous crystallization, or stalactite. Where 

 the interstices are large, there are vacant spaces, and the surfaces of all such 

 cavities are covered with granulated crystallization about -uof an inch thick. This 

 crystallized crust, no doubt, was deposited from the water passing through the 

 cavern in which the bones had been lodged; and by soaking through the porous 

 substance of every bone, the water had likewise deposited a crust of the same 

 nature, but much thinner, on all the internal surfaces of the hollow and spongy 

 bones. The bones were not in any other sense petrified. 



XXXIV.* Difficulties in the Newtonian Theory of Light, Considered and Re- 

 moved. By the Rev. S. florsley, LL.B., F.R.S. p. 417. 



Dr. Franklin, in a letter to a correspondent at New York, the 23d of that 

 valuable collection with which the public was obliged in the latter end of the 

 year 1768, proposes some objections to the Newtonian theory of light. His 

 words are these: ." I am much in the dark about light. I am not satisfied with 

 the doctrine that supposes particles of matter called light, continually driven off 

 from the sun's surface with a swiftness so prodigious. Must not the smallest 

 particle conceivable have, with such a motion, a force exceeding that of a 24- 

 pounder discharged from a cannon? Must not the sun diminish exceedingly by 

 such a waste of matter, and the planets recede to greater distances by the lessened 

 attraction? Yet these particles, with this amazing motion, will not drive before 

 them, or remove, the least and lightest dust they meet with: and the sun, for 

 aught we know, continues of his ancient dimensions, and his attendants move in 

 their ancient orbits." 



Dr. Franklin's questions are of some importance, and deserve a strict discus- 

 sion. On the supposition that light is a copious emanation of innumerable small 

 particles of matter from the sun, I had once occasion to inquire, what the force 

 of motion produced in every such emission could possibly amount to at the ut- 

 most. For this purpose, I made an estimate of the greatest probable magnitude 

 of the particles of light; and of the greatest density of each. I likewise com- 

 puted the greatest number of such particles, that could possibly fly off at once 

 from the surface of the sun ; supposing the sun's horizontal parallax to be no 

 more than 8'. These computations, with an account of the principles on which 

 they were founded, having been already given to the public;* I shall make use 



• In a little treatise, entitled, the Power of God, dedueed from the computable instantatieou» 

 productions of it in the solar system. — Orig. 



VOL. xm. K * ■' 



