Ml*. Jago on Ocular Spectres and Structures. 55 



virtue of which three molecules of sesquioxide may suifer reduction 

 as if they were only one molecule, and divide into two molecules of 

 the magnetic oxide, we might conceive a peculiar structure in the 

 Fcg Oj, with a tendency to separate again into FeO, Fcg O3 ; that it is 

 really in combination as Fcg O^, but ready to yield to slight causes 

 and become FeO, Fe2 O3. This would explain Mr. Mercer's experi- 

 ment (quoted by Brande, I. 716, edition 1848) of the chemical union 

 of a mechanical mixture of protoxide and peroxide of iron. 



Perhaps the sesquioxides occupy a middle place in the scale of 

 effects. Take the case of iron ; we have 



Fe + 0. pyrophorus, — violent oxidation, 

 Fe2O3+ITH3 + 0. alternate reduction and oxidation, 

 Fe O3 + NII3 (in water), reduction. 



To show the last, add ammonia to a solution of FeOy, KO, and 

 Fe.2 O3 will be precipitated. 



A mixture of ten parts hy weight of powdered chlorate of potassa 

 with one part of Fe., O3 disengages oxygen with extreme facility and 

 great ogconomy of heat as compared with the oxides of copper and 

 manganese ; and it is the more convenient because n grains of the 

 mixture will represent almost exactly n cubic inches of disengaged 

 oxygen. 



A state of mechanical division is not absolutely necessary for the 

 catalysation of some inflammable vapours by Fcj O3 ; an old nail, 

 entirely transmuted into rust, will perform the operation ; and M'hen 

 we consider that in many cases of fermentation, decay and putrefac- 

 tion, this oxide may be present, divided or aggregated, while heat is 

 evolved, and inflammable gases and vapours are set free, we may 

 hereafter be able to trace some instances of " spontaneous com- 

 bustion " to the catalytic action of the sesquioxides of iron. 



" Ocular Spectres and Structures as Mutual Exponents." By 

 James Jago, A.B. Cantab., M.13. Oxon. 



The present communication is a revised and modified version of a 

 paper bearing the same title, which was read on the 18th of January 

 and 1st of February, and which was, by permission, withdrawn. The 

 chief modification applies to the author's views respecting the struc- 

 ture of the vitreous body as deduced from entoptical phaenomena. He 

 is now of oj)inion that the arborescent system of which he infers the 

 existence in that part of the eye (Phil. Mag. vol. ix. p. 305) does not 

 consist oi tubes filled with globules or cells, as he at first supposed, but 

 of cell-constituted filaments. In a note, dated March 27, 1855, he 

 gives the following enunciation of his present views as to the struc- 

 ture of the vitreous body : — 



" In the vitreous humour are innumerable transparent globules, 

 beads or cells, of less specific gravity than the fluid, extremely 

 minute, and of uniform size, which are arranged, without exception, 

 in rows to form the threads of a lax, elongated, irregular web, 

 springing from the general surface of the capsule by, commonly, 

 exquieitely small meshes, and extending into the interior by others 

 of iucreasing uze, so that the innermost part of the web— which lies 



