Personal and household arrangements in relation to health : including hints with respect to the use of gas, gas-stoves, and of modern wall-papers / by John Angell.
- Angell, John
- Date:
- 1880
Licence: Public Domain Mark
Credit: Personal and household arrangements in relation to health : including hints with respect to the use of gas, gas-stoves, and of modern wall-papers / by John Angell. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
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![by dividing the upper part of the chimney into two halves, down one of which a current of cool fresh air descended to support the combustion of the candle, and tip the other of which ascended a current of hot air, conveying away with it the products of com- bustion, which, unless quickly removed, would suffocate the flame. May I ask all here, who now see me perform this simple experiment, to repeat it at home, and ponder over the important truths it conveys ? But in addition to the gaseous constituents of the air, to which I have already drawn your attention, there are always, under ordinary circumstances, present in it, floating through its mass, a number of mechanical impurities, of solid particles too minute to be visible in ordinary daylight. If I were to ask the various members of this audience individually whether they had ever seen light, or in other words, if light was visible, the answer, in at least nine cases out of ten, would be—yes. This, however, would be v/holly an error—light, though a cause of the visibility of surrounding objects, is itself perfectly //^visible. Light cannot itself be seen. I now want to ask you to perform an experiment, or rather to make an observation, which the circumstances of this lecture-room will not permit my bringing more directly before you. I want you, some bright sunny morning, when the sun is shining •directly on your windows, and before the shutters are opened, to go into a darkened-room, and placing yourselves on one side of the room, so as to look at right angles across the direction of the beams of light, which break their way through every crack or chink in the shutters, and carefully to observe what is there to be seen. You will imagine you see long straight lines of sunlight of various breadths and thicknesses stretching across the room, but you see no such thing. The light itself is ijivisibk, but what you do see is the powdered dust—the minute particles of so]id matter diffused everywhere through the atmosphere of the room, and rendered visible by the sunlight which accidentally falls upon them. Of what then do these solid particles, these mechanical impuri- ties, chiefly consist ? They consist partly of mineral matter, but chiefly of the dust of broken-up animal and vegetable matter, which, because of its greater lightness or buoyancy, continues to float longest in the atmosphere. Speaking more definitely of the impurities present in the atmosphere of our towns and cities we may describe them as consisting of—](https://iiif.wellcomecollection.org/image/b21450201_0015.jp2/full/800%2C/0/default.jpg)
