508 REPORT— 1889. 



il. Report of the Committee apjjointed to co-operate ivitli the Scottish 

 Meteorological Society in mahing Meteorological Observations on Sen 

 Nevis. — See Repoi'ts, p. 315. 



12. The Determination of the Amount of Hainfall} 

 Bij Professor Cleveland Abbe. 



A ri5sume of the general results of investigations on this subject was given. 



The deficit in catch by a gauge due to eddies of wind was shown on general 

 ireasoning to be proportional to the velocity of the wind, and to the relative per- 

 centage of small and slowly falling drops. 



Examination of the result, for many years at many places in the United States 

 and Western Europe, gives : — Average percentage deficiency = 6 times the square 

 root of the elevation of the gauge measured in metres. Combined with Archibald 

 and Stevenson's result, that for small altitude the wind-velocity is proportional to 

 the square root of the altitude, this confirms the conclusion that the deficiency is 

 proportional to the wind-velocity. 



Instead of using the coeiBcient 6 which is deduced from averages, it is better 

 "to use two gauges at different heights ; then if c is the catch by a gauge, P the 

 catch by a normal pit-gauge, /* the altitude of the mouth of the gauge, k the un- 

 linown coefficient to be used instead of 6, the above law gives 



.and if Cj, c.^ are the simultaneous catches of the gauges at altitudes Ji^, h^, the real 

 rainfall is 



PC, c„ 

 = c, + - 



The correction thus introduced is comparable with the differences on which 

 climatologists have had so much discussion, viz., as to the eflects of forests, build- 

 ings, time of day, cultivation of land, sunspots, &c. 



13. Hygrometrij in the ' Meteorological Journal.' By C. Puzzi Smyth. 



After noting the superior value officially attached to determinations of the 

 jmean temperature by observations of self-registering thermometers, recording its 

 maximum and minimum every twenty-four hours, the author inquires why the 

 .still more difficult problem of ascertaining the mean daily moisture of the atmo- 

 sphere is thrown over to a difierent principle of observing, long since condemned 

 for simple temperature. 



Believing that the want of good self-registering dry- and wet-bulb thermometers 

 for the purpose, was the chief obstacle, and having alighted on some recent makes 

 of Sixe's thermometers with their usual maximum and minimum registrations, as 

 well as several other very recommendable qualities, he invested two out of four of 

 •them with the peculiar fittings for wet-bulb hygrometers, after having made a table 

 of index corrections for them all, as dry thermometers, compared with a standard 

 thermometer. 



But as soon as hygrometric observations began, the depression of the wet, 

 below the dry, bidb always came out at only two-thirds of what a standard but 

 non-registering Glaisher arrangement gave out, for the horizontal form of Sixe ; 

 and no more than half, for a vertical form. 



These differences of hygrometric statement, though rather puzzling for a time, 

 were traced up to the wet-bulbs of the Sixe's thermometers bemg in contact on 

 one side with the scale-plate. For when that plate in the horizontal Sixe form 

 was cut entu-ely away from the bulb, and a new vertical form of Sixe was made 

 (per Mr. James Bryson, Edinburgh) with its long thm bulb wholly outside the 

 lest of the instrument, the indications of all three varieties of wet-bulb hygro- 



• American Meteorological Journal, vol. vi. 1889, pp. 241-2i8. 



