Is the Corona a Solar or a Terrestrial Phenomenon ? 117 



properties. For example, let chlorine, bromine, iodine, sul- 

 phur-vapour, or sulphuretted hydrogen act on thin layers of 

 silver; then layers of chloride, iodide, and sulphide of silver are 

 obtained, which in comparison with the metals and the metallic 

 oxides described are very transparent, and show in the spectro- 

 scope beautiful interference-bands. If, however, the intensity 

 or duration of the action of those agents exceeds a certain 

 limit, the structure of the layers is destroyed; the same are 

 then to be regarded as aggregates of many particles (in several 

 cases microscopic crystals), although they appear to the eye as 

 coherent masses ; they are more opaque than the metal itself, 

 and show no trace of interference-bands in the spectroscope. 



In reference to the chemical combination of the oxygen-com- 

 pounds of the heavy metals prepared by electrolysis, the follow- 

 ing result has been found : — Those compounds separated by the 

 current at the positive pole are not, as has hitherto been commonly 

 assumed*, peroxides, but definite hydrates of the same, which do 

 not lose their moisture under the air-pump. I believe I am able 

 to lay this down as a general proposition, as I have proved it for 

 the most different metals, namely lead, manganese, cobalt, bis- 

 muth, and antimony. The oxides and suboxides separated at 

 the negative pole are, on the contrary, always free from water, as 

 must be inferred from the examination of the electrolytic sub- 

 oxides of copper, bismuth, antimony, and oxide of iron, 



Berlin, October 1869. 



XV. On the Determination whether the Corona is a Solar or Ter- 

 restrial Phenomenon. By George M. Seabroke, Esq.f 



IT is my intention in this paper to attempt to show that, with 

 the existing state of our knowledge of the corona, the theory 

 set forth by Mr. Lockyer, that the corona is a terrestrial pheno- 

 menon, is quite possible, rather than to show that other theories 

 are wrong ; and further to demonstrate how the question may be 

 set at rest by observations on future eclipses. The points which 

 present themselves are as follows : — 



1. What are the facts with respect to the spectra of the corona 

 seen in past eclipses ? 



2. What spectra ought we to obtain from the corona on the 

 terrestrial theory during totality ? 



3. Are the spectra obtained from the corona in past eclipses 

 reconcilable with those we ought to get on the above hypothesis ? 



* Vergl. Wohler, '•'Ueherdas Verhalten einiger Metalle im el. Strom," 

 Nachr. der Kgl. Ges. d. Wiss. u. der G. Univ. zu Gbtt. 1868, No. 8. 



t From the Monthly Notices of the Royal Astronomical Society, June 10, 

 1870. 



