Spectrum analysis : six lectures, delivered in 1868, before the Society of Apothecaries of London / by Henry E. Roscoe ; with appendices, coloured plates, and illustrations.

  • Roscoe, Henry E. (Henry Enfield), 1833-1915.
Date:
1869
Catalogue details

Licence: Public Domain Mark

Credit: Spectrum analysis : six lectures, delivered in 1868, before the Society of Apothecaries of London / by Henry E. Roscoe ; with appendices, coloured plates, and illustrations. Source: Wellcome Collection.

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    mitted, and will soon render themselves evident to you. A current of cold water circulates through a double jacket on the outside of the cell, to keep the volatile disulphide cool. Now I think you will observe that no rays of light come through, but if I take a piece ol black paper, and place it in the focus of our mirror, you see the paper is ignited, owing to the presence of these dark heating rays. I may now do the same with a piece of blackened platinum (p, Fig. 6) ; you see that this also is heated to redness. I can show you this again in a variety of forms. Here is some gunpowder strewed on this paper ; you observe that it at once explodes when brought into the focus of the dark rays. Here I have some blackened gun-cotton, which instantly catches fire. I may vary the experiment by lighting a cigar; and here you see the brilliant scintillations of charcoal burn- ing in oxygen, having been heated up to the tempera- ture of ignition in the focus of the dark rays. Dr. Tyndall has measured the proportional amount of the entire heating rays which, pouring forth from this incan- descent carbon, has passed through this dark filter, and he has found that this consists of of the whole amount; so that only ^ of the radiation is really visible. Understanding then the existence in this ultra-red of a large amount of heating rays, let us pass now to consider the properties of the light which is given off* at the opposite or blue end of the spectrum, which I have called the chemically active rays. Allow me to show you an experiment to prove that it is in the blue portion of the spectrum that we have essentially these chemically active rays. In order to render the illustra- tion more perfect, I will first make an experiment with reference simply to white light, to show you that