REDUCING OBSERVATIONS.] 



METEOROLOGY. 



1169 



To find the weight of a cubic foot of air, the mean pres- 

 sure of the barometer being 29742 inches dry bulb 35 '8, 

 and wet bulb 34 5, 



In the hygrometrical table for 35. 



In column 13, the weight of a cubic foot of 

 air (the barometer being 29'0 inches) oppo- Grain. 

 site 34 wet, is 543 '4 



In column 14, the decrease of weight for an 

 increase of 1 in dry, is-l'l"; the propor- 

 tional part for 0-8, is . . . . -0'9 



In column 14, the increase of weight for an 

 increase in the reading of the barometer for 

 one inch, is + 18 '7 grains. 



Opposite 7 in the table, under 18 '7 in last 

 column, is ...... 



Opposite '01 in the table, in right-hand cor- 

 ner of the page, is 



542-5 



131 

 0-7 



The adopted weight of a cubic foot of air is . 556 '3 



To find the mean pressure of dry air, or that due to 

 the gases when separated from the water contained in 

 the air. 



Subtract the adopted elastic force of vapour (which is 

 the pressure of the water contained in the air) from the 

 adopted pressure of the barometer. 



Example. 



If the mean pressure of barometer be 

 And the elastic force of vapour is 

 The pressure of dry air (of tLat due to 

 the gases) will be .... 



29 -742 inches, 

 0186 inch, 



29 -556 inches. 



To find the monthly range of temperature, &c , deduct 

 the coldest temperature from the hottest observed during 

 the month. Thus 



Hottest temperature . . 60 '8 



Coldest temperature . . . 120 



Monthly range of temperature 



38-8 



To find the mean daily range of temperature, deduct 

 the mean of all the readings of the minimum thermo- 

 meter, from the mean of all the readings of the maximum 

 thermometer. 



41-0 

 30-4 



Mean maximum temperature . 

 Mean minimum temperature . 



Mean daily range of temperature . = 10 '6 



To find the amount of terrestrial radiation, deduct the 

 reading of a minimum thermometer, placed on the grass, 

 from that of a minimum thermometer, placed four feet 

 above the grass. Thus 



Greatest cold four feet above the grass 36 '5 

 Greatest cold on the grass . . 27 '8 



Amount of terrestrial radiation 



- 87 



To find the amount of solar radiation, deduct the 

 reading of a maximum thermometer (with a blackened 

 bulb) placed in full sunshine from the greatest heat in 

 shade. Thus- 



Greatest heat in sunshine 

 Greatest heat in shade . 



Amount of solar radiation 



59-3 

 >34-l 



25-2 



To find the greatest heat and greatest cold of the wet 

 bulb thermometer. This is obtained by attaching the 



VOL. I. 



muslin and cotton conductor to self-registering thermo- 

 meters, instead of to the ordinary thermometer. Thus- 

 Greatest cold of dry bulb . . 34-0 

 Greatest cold of wet bulb . . 32 '5 



Difference 



Greatest heat of dry bulb 

 Greatest heat of wet bulb 



Difference 



1-5 



46-7 

 42-8 



3-9 



To find the range of temperature of the wet bulb ther- 

 mometer, deduct the greatest heat from the greatest cold 

 recorded. Thus 



Greatest heat 42-8 



Greatest cold 32-5 



Range of wet 10'3 



To find the mean amount of cloud. 



This, by practice, is accomplished very accurately by 

 estimation, 10 being considered an overcast sky, and a 

 cloudless sky. It must be remembered, in making the 

 estimate, that, with a partially covered sky, the forms 

 of the clouds, and the space they cover, are only cor- 

 rectly seen in the zenith ; the nearer the horizon we 

 approach, the more obliquely do we look upon them ; 

 and, consequently, near the horizon, the sky will appear 

 to be more overcast than it is in reality. The observer's 

 judgment should, therefore, be more especially confined 

 to the upper half of the sky. 



Observations made at 9 A.M. and 10 P.M., December, 

 1855. 



Sum of all the estimates at 9 A.M., 2158; and at 

 10 P.M., 2024. 



31)2158( 6-96 mean at 9 A.M. 



186 O'lO cor. for diurnal range. 



298 6-86 corrected amount. 

 279 



190 

 186 



. .4 

 3l)2024( 6 -5 mean at 10 P. M. 



186 +0-2 cor. for diurnal range. 



164 67 corrected amount. 

 155 



..9 



Corrected reading at 9 A.M. 6 '9* 

 Corrected reading at 10 P.M. 67 



Sum of the two series 2)13 '6 

 Adopted mean amount of cloud . . 6 '8 



CLASSES OP CLOUDS. Mr. Luke Howard, the well- 

 known meteorologist, was the first to classify the clouds ; 

 and these classes have been very conveniently abbreviated 

 by Mr. Glaisher. They are 



Cirrus = cL 



Cumulus 

 Stratus 



cu. , 

 st. 



Cirro-cumulus = ci.-cu. 



Cirro-stratus 

 Cumulo-stratus 



Nimbus 

 Scud 



ci.-st. 

 cu.-st. 



ni. . . 

 so. . . 



feathery looking, the most 



lofty cloud, 

 mountainous looking, 

 the ground-cloud forms at 



sunset, and disappears at 



sunrise, 

 rounded masses, or woolly 



tufts. 



horizontal masses, 

 an accumulation of cumuli, 

 sometimes fungus-shaped, 

 rain-cloud, 

 broken, ilying nimbi. 



7K 



