WEATHER REGISTRATION.] 



METEOROLOGY. 



1189 



frequently, the highest point of a mountain range is so 

 completely hidden by surrounding but lower peaks, that 

 an observation for taking the requisite angles is not 

 possible. It also often happens that the summit of a 

 mountain is almost constantly covered with, mist or, at a 

 portion of its height, such may be constant which equally 

 prevent the necessary trigonometrical observations. In- 

 dependently of these considerations, the barometer 

 affords a check on, and sometimes a verification of, 

 results obtained by other methods. At the present time, 

 our estimates of the height of many of the most extensive 

 ranges of mountains, in various parts of the world, 

 depend upon barometrical observations ; and, perhaps, 

 many of them require considerable modification before a 

 correct altitude can be obtained. Much difficulty arises 

 in the use of the ordinary mercurial instrument, owing 

 to its want of portability, and the necessity of the cor- 

 rections which have beeu pointed out : accordingly, some 

 of our leading instrument-makers have turned their 

 attention to the perfecting of the aneroid. One of these 



instruments, manufactured by Messrs. Negretti and 

 Zambra, has been used by Mr. Glaisher in his balloon 

 ascents ; and he considered that it might be depended on 

 at a pressure equal to one indicated by five inches of 

 mercury. As our highest mountains have an elevation 

 at which a much taller mercurial column is supported, it 

 is probable that such instruments may be of great service 

 for the purpose, as substitutes for the barometer. 



The following table will be of great utility, both for 

 the purpose of measuring heights by the barometer, and 

 for adjusting the level between two places where baro- 

 metrical observations are being carried on. The barome- 

 tric column is supposed to stand at a height of 31 inches, 

 at the sea-level. For any other barometric height at the 

 sea-level, at the moment of observation, an allowance 

 for the difference above or below 31 inches must be 

 made ; which is, of course, readily done by the rules 

 of common proportion. The table is copied (but cor- 

 rected) from the Barometer Manual of the Board of 

 Trade. 



DIFFERENCE TABLE FOE ELEVATIONS. 



GHAUTS FOR WEATHER REGISTRATION. Instructions, 

 of a very detailed character, have already been given in 

 Chapter IV., as to the method of making observations by 

 the barometer and thermometer ; the precautions which 

 must be taken ; corrections to be made, itc. Many of 

 our readers, however, may be disposed not only to register 

 their observations in a book, for subsequent reference, 

 but also feel desirous of adopting some plan by which 

 they may possess * general and combined view of the 

 barometric and thermometric changes that occur monthly ; 

 BO that, by mere inspection, they may be able to trace 

 the variations which have occurred. One of the best 

 plans which we have yet seen, i that recommended and 

 used by the Meteorological Department of the Board of 

 Trade, and of which a specimen is given in the folio 

 plate. By an ingenious contrivance, both the barometric 

 and thermometric ranges are marked down on one 

 diagram. 



The sheet is divided by vertical and horizontal lines, 

 between which the daily ranges are to be marked with 

 dots and lines. On the left hand, a scale ascends, which 

 is divided so as to indicate the height of the barometer 

 from 28 to 31 inches. This is sub-divided into tenths ; 

 and these, again, may be easily reduced to halves, &c., 

 in marking the height. On the right, the thermometric 

 range is denoted, running from 20, or 12 below freezing 

 point of Fahrenheit's scale, to 80. The horizontal lines 

 are crossed by vertical dark lines, with an intermediate 



lighter one each entire division being intended to denote 

 a day. Thirty-one and a-half are provided ; so that the 

 first three half divisions may be used for the last day and 

 a-half of the previous month a method which is useful 

 for "forecasting," for reasons mentioned at a previous 

 page.* It will be seen that two observations, at least, 

 both of the barometer and the thermometer, may thus be 

 marked on the lines daily ; and by dividing the inter- 

 mediate spaces, even more may be mapped down. 



The method of using the diagram is as follows : Sup- 

 posing that the barometer stands at 29 '50, on the first 

 day of the month. Look to the left hand scale, and 

 trace, by the eye, the horizontal line from 29 '5 to the 

 vertical dark line running downwards from the figure 1, 

 at the top of the scale. Make a dot at the point where 

 they intersect the height of the barometer will thus bo 

 indicated at the time the observation is made, which 

 should be at 8 A.M., that affording the best daily average. 

 If another observation be made at 8 P.M. that is, at an 

 interval of twelve hours proceed in the same way, for 

 any height, and mark a dot where the horizontal line 

 intersects with the light vertical line, which will be half- 

 way between 1 and 2, as marked on the top of the scale. 

 Draw a straight line, connecting the dot of the morning 

 and that of the evening observations thus the dots will 

 indicate the actual heights, whilst the line will show the 

 course of variation in twelve hours. On the 2nd of 



See ante, p. 1176. 



