MADE AT MARIETTA, OHIO. 



31 



Mean Range of ilie Diurnal Fluctuation for each Month. 



The observing hours noted in Table IV are sufficiently near the times of the 

 morning and afternoon extreme temperatures to deduce from this record the diurnal 

 range. For this purpose we multiply each observed range with a factor deduced 

 from the Philadelphia series of hourly observations.^ To the table of monthly 

 mean diurnal ranges at Marietta I have added for comparsion values similarly 

 deduced from 51 years of observations at Brunswick, Me., latitude 43° 54.'5. 





Observed difference. 



Factor. 



Marietta diurnal 

 range. 



Brunswick diurnal 

 range. 



January . . . . . 



February 



Marcli ...... 



April 



May . . - . 



June ...... 



July 



August 



September ..... 

 October ..... 



November 



December ..... 



11°.90 



13.92 



17.45 



21.17 



20.08 



16.55 



16.32 



16.54 



17.66 



17.75 



14.88 



10.87 



1.01 

 1.03 

 1.07 

 1.08 

 1.12 

 1.16 

 1.13 

 1.07 

 1.06 

 1.05 

 1.04 

 1.03 



12°.0 

 14.3 

 18.7 

 22.8 

 22.5 

 19.2 

 18.4 

 17.7 

 18.7 

 18.6 

 15.5 

 11.2 



13°.7 

 15.2 

 16.0 

 15.7 

 17.7 

 18.4 

 20.2 

 19.1 

 17.4 

 15.0 

 11.4 

 11.8 



Year 







17.5 



16.0 



At Marietta the diurnal range attains its greatest value in April, and its least 

 value in December ; there is also an indication of a secondary minimum in August, 

 and of a secondary maximum in September or October. In April the range is more 

 than double the amount observed in December. The range, in general, appears 

 rather large, which may possibly be due to a position of the thermometer not suf- 

 ficiently sheltered from radiation. 



Direction of the Wind. 



The materials for the discussion of the wind are taken from Dr. HUdreth's re- 

 cord; it extends with tolerable completeness over the years 1829 to 1850 inclusive; 

 the record for 1852-53-54 and 1858-59 is, in some months, less complete. During 

 these 27 years for which the original record is preserved, the direction of the wind 

 was, in general, observed once a day; but it appears, whenever an important 

 change in the direction took place during the day, two and even three entries a 

 day were made. The precise- hour when the direction of the wind was recorded is 

 not, given, but this is of little consequence since the average direction during the day 

 is set down. There is no entry for calms, and the directions stated may be taken 

 to refer to the true meridian (the magnetic meridian difiers but 1° or 2° from the 

 true one). 



The method and formulae for the reduction and force of the wind are the 

 following : — 



Let Qi d^ Q3 ..... he the angles which the direction of the wind makes with 

 the (true) meridian, reckoned round the horizon, from the south westward to 360°, 



Tables, meteorological and physical, prepared for the Smithsonian Institution by Prof. A. Guyot. 



