258 



OHIO BIOLOGICAL SUKVEV 



cloudy 131, and cloudy 181. The average number of days with thunder- 

 storms at Cohunbus is 83." 



The prevailing" winds at ('olunil)us ai'e southwest and the average 

 movement of air is eight miles per hour. Tornadoes are rare, but 

 storms violent enough to destroy many trees are of p^^riodical occur- 

 rence. The records of the Weather Bureau show that during the years 

 1892-1001, when the observing station was located in a comparatively 

 low building, there averaged 3.4 days per annum with winds reaching 



la^s*-*^ 



Fig. 3. Over the Upland Between Big Pine Creek nnrt (jueer Creelv. 

 Timber remains only in the r;ivines. 



or exceeding 40 miles per hour. But from 1003 to 1911, after the 

 observatory was moved into a "skyscraper," the average number of 

 days with gales ]*ose to 26.5. The absolute maximum is 70 miles per 

 hour on March 15, 1908. 



The mean relative humidity at Columbus is as follows : 



On the longest days of the year there are about 15 hours of sun- 

 shine from sunrise to sunset. 



