408 
The Ohio Naturalist. 
[Vol. XV, No. 3, 
On the 15th the predicted temperature would be 34, while 
the thermometer reached 33. On the Kith and 17th the exact 
minimum would have been predicted. 
Rules to follow. The average time of this median hour will 
vary under different weather conditions, at different seasons of 
the year, and in different localities. Outside of the cities, in cen¬ 
tral Ohio, under conditions of clear skies and comparatively still 
air, it will be close to the following. 
April, 7:15 p. m.; May and June, 7:30 p. m.; September, 
6:30 p. m.; October and November, 6 p. m. In July it is about 
7:30 p. m., ajid in August, 7 p. m. 
If a strong wind is blowing in the afternoon or if the afternoon 
is cloudy or partly cloudy, and the wind goes down and it clears 
off in the night the time of the median temperature will be from 
30 to 45 minutes later than the average given. 
If it should cloud up during the night after a clear afternoon 
and evening the minimum temperature will not be quite so low 
as is indicated by the median. 
In cloudy and stormy weather, or when strong southerly winds 
prevail, or if the wind is high from the northwest the time of the 
median varies so much that no attempt should be made to make 
predictions from it. 
This is especially true when after a period of warm weather 
the wind shifts to northwesterly and the temperature begins to 
fall rapidly. This indicates the approach of a cool area and the 
only way to estimate the probable minimum temperature is from 
the daily weather maps. 
But after the windy front of this cool wave has passed by and 
the air is clear and still and the days are warn and the nights 
cool and frosts threaten then the plan can be used. 
Reliable maximum and minimum thermometers should be 
obtained and exposed in a lattice work shelter where the air 
circulates freely and the sun will not strike the instruments. 
The difference in temperature between that at the average 
half-way or median hour should be subtracted from the highest 
during the day and the difference subtracted from the reading at 
the half way hour. The remainder will show the approximate 
lowest temperature during the coming night. 
Records that are at hand indicate that the average time of 
median will be slightly later in the valleys than at higher elevations, 
but each man interested should be able to determine his own 
median hour by careful records of the temperature. 
The Weather Bureau office at Columbus will continue its study 
during the coming year at a larger number of stations than were 
in operation last year. 
