METEOROLOGY. 



575 



will be carried to and fall at the lee side of the 

 obstacle. A first corollary from this reasoning 

 is, that, did the instrument or its support cause 

 no disturbance in the wind, no deficiency of 

 rain would appear. But only a gauge with its 

 mouth level with the ground can fulfil this 

 requirement. And in the case of elevated 

 gauges, it is probable that the house or tower 

 causes the chief part of the deficiency in the 

 rain caught. [Another consequence is, that in 

 absolutely calm rains, if the view taken be cor- 

 rect, the deficiency in the elevated gauge should 

 not appear.] 



A number of facts confirmatory of the view 

 given are then presented. Mr. H. Boase, of Pen- 

 zance. July, 1822, having observed the quantity 

 of rain caught in gauges on the ground and hi 

 an elevated position, concludes that " the differ- 

 ence of the quantity of rain caught in a gauge 

 placed on the top of a building, and one at the 

 level of ground, is, for some reason or other, 

 proportional to the velocity of the wind." The 

 measurements given by Luke Howard, when 

 arranged in the order of difference of quantity 

 of rain caught at the same times in higher and 

 lower gauges, are also found to be arranged 

 exactly in the order of the force of the accom- 

 panying wind, as given in notes annexed. 

 Thus, in rains attended with a strong wind, 

 the ratio of difference in the two sets of gauges 

 is from 3 : 1 down to 1.75 : 1 ; in those with 

 light and scarcely noticeable winds, it is from 

 1.6 : 1 down to an equality in the two. The 

 continued meteorological observations at Green- 

 wich Observatory and elsewhere, exhibit an ex- 

 treme irregularity and discordance in the re- 

 sults of measures of fall at different heights, 

 showing at least that in a case of this sort we 

 cannot appeal to average results, but must have 

 specific, careful observations. Yet many indi- 

 vidual instances are found in the Greenwich 

 records which corroborate the position taken. 

 Prof. Phillips, for some time in charge of the 

 observatory named, himself remarks that a 

 great deficiency in the upper gauge was a 

 phenomenon of wintry character ; and as a rule 

 the deficiency is more marked in March than 

 in any other month. Dr. Trail and Mr. Meikle 

 referred the difference in some way to action 

 of the wind ; and the latter nearly anticipated 

 Jevons' views. Prof. A. D. Bache, in a paper 

 before the British Association, 1838, on the 

 effect of deflected currents of air, and the quan- 

 tity of rain collected by rain gauges, showed 

 by experiments the immense difference that 

 may occur between gauges placed at the differ- 

 ent angles of the same building ; and he found 

 also that the gauges to leeward received gene- 

 rally more rain than those to windward. 



In another way. reasoning from the known 

 conditions of the air in higher and lower strata, 

 in reference to temperature and saturation, Her- 

 schel has shown that within the last 213 ft. of 

 the ground not more than T '.-th of the quantity 

 of rain to be accounted for could possibly be 

 added to the fall. Mr. Jevons proceeds to pro^e 



that even Herschel's allowances on this score 

 are too liberal, and that under no circumstances 

 will the increase of falling rain within the last 

 few hundred feet be more than almost infinites- 

 imal. In fact, distant showers of rain are of- 

 ten observed which evaporate and vanish be- 

 fore reaching the ground ; but no observations 

 of the reverse character are known. A second 

 argument in favor of increase of rain near the 

 earth, drawn from the fact that the internal 

 supernumerary fringes of rainbows are only seen 

 in the upper parts of the bows, never near the 

 earth, and as proved by Dr. Young, are only 

 producible where the drops are of equal size, is 

 readily disposed of by remarking that the re- 

 quirement in respect to the drops is equality 

 of size, not any given size ; and the jostling of 

 drops together by the wind, or either increase 

 or decrease of some of the drops more than 

 others, could alike give rise to the want of 

 uniformity which seems to characterize the 

 drops near the earth. 



From the conclusions reached, it further fol- 

 lows that all observations by means of elevated 

 or exposed rain gauges must be rejected as fal- 

 lacious or useless. And the most unexception- 

 able rain gauge of the common kind, would be 

 a sheet of metal, say 10 feet square, spread flat 

 upon the ground in an open place, with a sim- 

 ple collecting vessel let down in its centre, and 

 the edges of which should not rise more than 

 an inch above the plate. In this there would 

 be no appreciable loss by wind, nor irregularity 

 from splashing. The water collected in such 

 vessel should be conveyed by a pipe running 

 from it below to a sunken reservoir or record- 

 ing apparatus. u Philos. Magaz.," Dec., 1861. 

 It may here be added that the new rain 

 gauge, or pluvioscope, of M. Herve Mangon, 

 of Paris, could doubtless be so arranged as not 

 to present an obstacle by rising above the gen- 

 eral level of the ground. This Consists of a 

 long strip of paper, prepared with solution of 

 sulphate of iron, and after drying, rubbing with 

 finely powdered galls, so that each drop of ram 

 falling on its surface will produce an ink and 

 so leave a black spot, this paper to be gradually 

 unrolled by clockwork, so that in the course 

 of 24 hours every part of it shall have been 

 exposed to the open air. The sheet of paper is 

 easily spaced for hours and minutes, and the 

 relative frequency of the spots on its different 

 parts shows the comparative, not the absolute, 

 rainfall in different parts of the time occupied 

 in unrolling it. 



Admiral Fitzroy^s System of Weather Fore- 

 easts. Storm Signal*, and Meteorological Tele- 

 graphy. President Fairbairn, in his opening 

 address before the British Association, 1862, in 

 course of allusions to the scientific and practi- 

 cal progress of the time, called attention to the 

 labors of Admiral R. Fitzroy and his coadjutors 

 in the collection of meteorological facts, and 

 the application of the principles of the science 

 to useful purposes. He stated that, in 1854, in 

 consequence of representations originating with 



