necessity for the application of any so-called corrections for daily range must necessarily lead to error. The comparison should also only be between observations made during the same years, since the means of different years often differ widely from each other. Thus the difference of height between two places at which barometrical observa tions were made, from 1830 to 1859 and from 1850 to 1869 respectively, could be more accurately ascertained from the ten years averages from 1850 to 1859 during which observations were made at both places, than from the longer averages of thirty and twenty years. Inattention to this point has of ten led to error, especially in cases where at one of the places only a few years were available. To secure greater accuracy, the calculations should be made on the mean for the year, the two extreme months, January and July, and that month during which the distribution of pressure is most uniform over the region where the places are situated. Owing to the great differences in the distri bution of atmospheric pressure in different parts of the globe (see Atmosphere), comparison of the observations at the higher station with those at more than one lower station is in some cases indispensable. Thus, if it were desired to compute the height of Dovre, in Norway, barometrically, it should be compared both with Christiania and with Christiansund on ths west coast; for if compared with Christiania alone the calculated height would be too high, and if with Christiansund too low, the reason being that the mean annual pressure diminishes from Christiania to Christiansund. The same remark applies to a large portion
of Hindustan and to many other regions of the globe.The more special precautions to be taken in deducing heights from one or a few observations, that is, from such data as travellers observe, are these : that the observations be made in as settled weather as possible, at those hours of the day, at least, at which observations are made at the nearest meteorological stations, and be repeated as long as possible from day to day; that the barometer hang perpendicularly and in shade ; and that the observations be not made till the whole instrument has acquired the tem perature of the surrounding air. For, for every degree which the temperature indicated by the attached thermo meter differs from the temperature of the whole instrument, there is an error of about O OOS inch.
From their portability and handiness the aneroid baro meter, and the thermometer for ascertaining the point at which water boils, are of great use in determining heights, the thermometer, if properly managed, being the more accu rate of the two. Since, owing to the sluggishness with which the aneroid often follows the changes of pressure, espe cially low pressures, its readings should not be recorded till it has hung for some hours at the place of observation, and if this be not possible, the time which elapsed from arriving at the place and making the observations should be stated. It may not be unnecessary to add that every opportunity which presents itself should be taken of comparing it with a standard mercurial barometer, owing to the variations, it-regular or permanent, to which aneroids are subject, and that the instrument should always be read in one position, since the difference between the reading in a horizontal position and the reading in a vertical position is often considerable.
At a pressure of 29-905 inches distilled water boils at 212. The temperature of the boiling point varies with the nature of the vessel. Thus, if the interior of the glass vessel be varnished with shell-lac, the temperature may rise to 221; and if iron filings be dropped into the water, the temperature is lowered. But in all these cases the temperature of the vapour arising from the water is as nearly as possible the same. Hence in making observations with the thermometer for hypsometrical purposes, the instrument is not plunged into the water, but the whclo instrument, bulb and stem, are by an apparatus used for the purpose plunged into the vapour arising from the boil ing water. The degrees on the thermometer used are greatly enlarged, thus admitting of a minute subdivision of the scale and, consequently, of very precise readings. The following are a few of the barometric heights corresponding to different temperatures at which distilled water boils, taken from Regnault s tables revised by Moritz:—
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Boiling Point. 211 210 209 208 207 206 Ban.meter. inches. 29-331 28-751 28-180 27-618 27 -066 26-523 Boiling Point. 205 204 203 202 201 200 Barometer. Inches. 25-990 2o 465 24-949 24-442 23-943 23-453
The temperature of the vapour of the boiling water being observed, the pressure is ascertained from the table, whence the height may be calculated, just as in the case of pressures obtained by means of a mercurial barometer.
The remark made by Sir John Leslie many years ago still holds good, that it is preposterous, in the actual state of physical science, to effect any high refinement in the for mula for computing barometrical heights. What is required on the part of the computer of heights from barometrical observations is carefully to weigh the limits of error due to the instrument and methods of observations, to the hour of the day and the month of the year (see Atmosphere, p. 28), and to the degree of unsettledness of the weather at the time the observations were made, and to give effect to these in the calculated results. From inattention to these simple considerations a large proportion of important heights given in works of travel and of physical geography are very errone ously stated, and consequently require careful revision.
For very rough approximations to the real height from observations of pressure and temperature, Sir G. B. Airy has prepared a table showing the differences of level corre sponding to differences of pressure. It is from this table that the heights corresponding to pressures engraved on many aneroids are usually taken. The heights read off from the pressures should be corrected for observations of tem perature carefully taken at the upper and lower stations, the mean of these two observations being assumed as the mean of the stratum of air occupying the interval between the two heights.
(a. b.)
BARON. The origin and primary import of this term have been much contested. Menage derives it from the Latin baro, a word which we find used in classical Latin to signify "a simple" or "foolish man" (Cic. Fin., ii. 23). Another form of the same word appears to be taro, to which Lucilius gives the meaning " a stupid man," " a blockhead," Forcellini observing that its primary sense is " a block of tough, hard wood." But with greater probability Graff derives the word baron from the old German Bar = Mann, freier Mann. The Avord seems related to the Spanish raron, which means " a male," " a noble person," and its root may be found in the Sanskrit rera. Like the Greek urijp and the Latin vir, the word baron signifies man in general and also a husband the old legal expression baron and feme being equivalent to our ordinary phrase "man and wife."
to a member of the lowest order of the peerage, but in ancient records (as Lord Coke observes) the barony included all the (titular) nobility of England, because all noblemen were barons though they might possess a higher dignity also ; and the great council of peers, in which were included dukes, marquesses, and earls, as well as barons, was styled
simply the " Council de Baronage." In like manner we