UM 



METEOROLOGY. 



[KBDCCUCQ OBSBBVATIONS. 



That the formula become* 



0-0001001 X (-32) - 0-000010434 X ft -62) 

 1+OO001001 X (t-32) 



3rd. Table of Correction* to be applied to Mtttoroloyical 

 (Mmrtationi for Diurnal hangr, prepared by the Council 

 of the British Meteorological Society. These tables aro 

 of the utmost importance, as they enable an observer, 

 from one, two, or three readings daily, to find from them 

 the true monthly means ; in fact, to make his observa- 

 tion* represent a reading taken every hour, day and 

 niL'lit. Thus, if a reading of the barometer be made 

 daily at 3 A.M. ill March, the mean will be -023 too low, 

 or, at 11 A.M., -015 too lii^li. The necessity of this 

 reduction becomes very evident from hourly readings of 

 tin- thermometer; for, suppose the readings are made 

 in June, at 4 A.M., the meau will be 9-3 too low, or, if 

 at 2r.M., 8-6 too high. 



The only correction requisite for the reduction of me- 

 teorological observations not found in the three alx>ve- 

 mentioned tables is that for capillarity the capillary 

 action of the tube of a barometer depressing the mer- 

 cury by a quantity inversely proportional to the diame- 

 ter of the tube. The following table will be found suffi- 

 cient for this reduction : it is copied from the work pub- 

 lished by the Committee of Physios and Meteorology of 

 the Royal Society : 



Correction to be adtled to Barometer Readings for 

 Capillary Action. 



Diunrtrr 



of tube. 



Inch. 



0-GO 

 050 

 045 

 040 



Onrr'-ction for 



unboil.il tubes. 



Inch. 



Correction for 



boiled tubct. 



Inch. 



+ 0-004 + 0-002 



01J07 0-003 



0-010 0-005 



0014 0-007 



0020 0010 



030 0-028 0-014 



0-25 0040 0020 



0-20 OOGO 0-029 



0-15 0-088 0-044 



0-10 0-142 0070 



The following reductions for meteorological observa- 

 tions will supply examples of every reduction necessary: 

 BABOMBTER REDUCTIONS. To find the mean pressure 

 of the barometer for the month of February, 1856 

 (height above the sea-level, 281 feet). 



Sum of all the readings made at 9 A.M., 867640 ; 



at 10 P M., 867528. 

 Divide the above by the number of observations. 



29)867640(29 -918 inches, 29)867528(29 -915 inches. 

 58 58 



287 

 261 



266 

 261 



54 

 29 



233 



287 

 201 



265 

 2J1 



42 

 29 



138 

 145 



-18 -7 



Sum of all the readings of the attached thermometer 

 at 9 AM., 13435 ; at 10 P.M., 13745. 



29)13435)46 -3 temp, of mercury. 

 116 



183 

 174 



M 



87 



29)13745(47-4 temp, of mercury. 

 110 



214 

 203 



115 

 110 



-1 



Mean pressure at 9 A. M =20018 



Correction for temperature of 46-3 . . = O47 



Mean pressure corrected for temperature 

 Index error . ... 



Mean pressure further corrected for index 

 error 



Corrections for capillarity, the mercury being 

 boiled 



Correct reading for 9AM 



Correction for diurnal range for February . 



Approximate mean pressure ... 



Mean pressure at 10 P.M. . . . 

 Correction for temperature of 47 '4 



Mean pressure corrected for temperature 

 Index error 



= 29-871 

 -002 



29-869 

 + -002 



= 29-871 

 -008 



Mean pressure further corrected for index 

 error . 



Correction for capillarity, the mercury being 

 boiled 



Correct reading for 10 P.M 



Correction for diurnal range for February . 



Approximate mean pressure ... 

 Ditto. ditto. 



= 29-863 



= 29-915 

 = -050 



29-8IM 

 002 



= 29-863 

 + -002 



29-865 

 -007 



29-8.18 

 29-803 



Sum of the two observations . . . 2)59-721 

 Adopted mean pressure for the month . 29-8605 



To reduce the mean pressure of the month to the sea- 

 level, the adopted mean temperature of the air being 

 36 0, and the cistern of the barometer 281 feet above 

 the level, the adopted mean pressure = 29-860 inches. 



In Table 2 of Olaisher's Hygrometrical Tables (page v.), 

 showing the volume of a mass of dry air, after expansion 

 from heat, for each degree of Fahrenheit's scale, it will 

 be seen that a stratum of air 90 feet in thickness, will 

 balance a column of mercury O'l inch in height. 



The factor for 36 is 1 -008 

 Multiply this by 90 ft. 90 



feet. 



90-720= 90-7)281-0(-3098ofanin. 

 2721 



8900 

 8163 



7370 

 7256 



114 



Adopted mean pressure for altitude of 281 feet 29-860 

 Correction to reduce to sea-level . . . + -310 



At sea-level the mean pressure is 



In. left. 28' 



As 90-7 : 0-1 : : 281 : - - 



30 170 in. 



- 0-310. 



