Copy 2

A complete course of meteorology / By L.F. Kaemtz ... with notes by Ch. Martins ... and an appendix, containing the graphic representation of the numerical tables, by L. Lalanne ... Translated, with notes and additions by C.V. Walker.

  • Ludwig Friedrich Kämtz
Date:
1845
Catalogue details

Licence: Public Domain Mark

Credit: A complete course of meteorology / By L.F. Kaemtz ... with notes by Ch. Martins ... and an appendix, containing the graphic representation of the numerical tables, by L. Lalanne ... Translated, with notes and additions by C.V. Walker. Source: Wellcome Collection.

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    The thermometers that are employed in meteorological observations are generally those made with mercury ; for this metal does not freeze except at very low temperatures, such as are never observed in our climates. But, for a wintering in high latitudes, spirit thermometers must be provided. Ifthe freezing and the boiling points are deter- mined on such an instrument, and the interval is divided into 80 or 100 equal parts, its variation will not be parallel to those of a mercurial thermometer; this is due to the unequal dilatation of the two liquids. Therefore, in com- paring a spirit with a mercurial thermometer, a correction must be made through the whole extent of the scale. It is often essential to know the highest and the lowest degrees marked by the thermometer, in a certain determined interval of time. To effect this we have re- course to thermometrographs. Of the different arrange- ments that have been given, the following is the simplest, and perhaps the best. If a mercurial thermometer is placed horizontally, and a movable index of iron wire, or of glass is in contact with the extremity of the mer- curial column, this index will be thrust forward as the mercury expands, but will remain at the same place if it contracts under the influence of a reduction of tempera- ture.* The point of the scale where the index is found in- dicates, therefore, the greatest degree of heat, or the mazi- mum to which the instrument has been subjected. An an- alogous mechanism will give us the lowest degree to which the instrument has fallen. At the extremity of the column of a spirit thermometer a glass index is so placed that it is entirely plunged into the liquid. When the alcohol con- tracts, it draws with it the index, in consequence of its ad- hesion to the glass, but, in expanding, it does not displace it; so that the degree, corresponding to the point where the index is found, indicates the minimum, or lowest tempera- ture, to which the instrument has been exposed. If, then, we wish to know the mazimum and the minimum of the temperature in the twenty-four hours, the index of iron wire is placed in contact with the mercury, and the upper extremity of the glass index is made to coincide with the extremity of the column of spirit, by inclining the two instruments. The following day the position of the * Indices of glass, and even those of iron wire, in the course of time, are drowned, that is, they penetrate into the mercury. To avoid this inconve- nience, M. GREINER crowns the thermometric column with a cap of very thin glass, by which the mercury is kept from the index.—M.
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