On the Behaviour of Thermometers in a Vacuum
Proceedings of the Royal Society of London
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... out Early Journal Content at http://about.jstor.org/participate--jstor/individuals/early-journal--content. JSTOR is a digital library of academic journals, books, and primary source objects. JSTOR helps people discover, use, and build upon a wide range of content through a powerful research and teaching platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not--for--profit organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please contact firstname.lastname@example.org. 1869.] On the Behaviour of Thermometers in a Vacuum. 1869.] On the Behaviour of Thermometers in a Vacuum. experiments; the case of toluol may be taken as representative of a great number of others. The specific gravity of this liquid is 0'85, that of water being unity; the specific gravity of its vapour is 3'26, that of aqueous vapour being 0'6. Now, as the size of the cloud-particle is directly proportional to the specific gravity of the vapour, and inversely proportional to the specific gravity of the liquid, an easy calculation proves that, assuming the size of the vapour polyhedra in both cases to be the same, the size of the particle of toluol cloud must be more than six times that of the particle of aqueous cloud. It is probably impossible to test this question with numerical accuracy; but the comparative coarseness of the toluol cloud is strikingly manifest to the naked eye. ' The case is, as I have said, representative. In fact, aqueous vapour is without a parallel in these particulars; it is not only the lightest of all vapours, in the common acceptation of that term, but the lightest of all gases except hydrogen and ammonia. To this circumstance the soft and tender beauty of the clouds of our atmosphere is mainly to be ascribed. The sphericity of the cloud-particles may be immediately inferred from their deportment under the luminous beams. The light which they shed when spherical is continuous: but clouds may also be precipitated in solid flakes; and then the incessant sparkling of the cloud shows that its particles are plates, and not spheres. Some portions of the same cloud may be composed of spherical particles, others of flakes, the difference being at once manifested through the calmness of the one portion of the cloud, and the uneasiness of the other. The sparkling of such flakes reminded me of the plates of mica in the liver Rhone at its entrance into the lake of Geneva, when shone upon by a strong sun.