ACTIVITY 
NOON 6 PM MIDNIGHT 6 AM NOON 
AT LEAST ONE NIGHT OF PAIR WITH TEMPERATURE ABOVE 55° F. 
6 NIGHTS OF INCREASING BAROMETRIC PRESSURE 
6 NIGHTS OF DECREASING BAROMETRIC PRESSURE 
BOTH NIGHTS OF PAIR WITH TEMPERATURE BELOW 55°F 
20 NIGHTS OF INCREASING BAROMETRIC PRESSURE 
20 NIGHTS OF DECREASING BAROMETRIC PRESSURE 
Figure 101 — Periodicity of activity during nights of continouusly increasing barometric pressure in contrast to that during 
nights of continuously decreasing barometric pressure. Barometric pressure appears to affect activity much less than does 
the accompanying changes in temperature. 
in activity after midnight on the nights of increasing 
barometric pressure, but this may be entirely 
accounted for by the greater decrease in tempera- 
ture. The only possible effect that barometric 
pressure might exert is that activity changes are 
induced to vary in the same direction as baro- 
metric pressure. If this is true it might account for 
the lack of a greater inhibition of post-midnight 
activity by the greater decrease of temperature on 
those nights with a continuously rising barometric 
pressure ffigs. 100B and 101B). An indication of 
this type of effect may be from the fact that, on 
13 out of the 21 pairs of days between which there 
was less than a 2.0° difference in mean night tem- 
perature, but 0.1 inch or more difference in baro- 
metric pressure, the change in intensity of activity 
varied in the same direction as barometric pressure. 
It will probably take carefully controlled labora- 
tory studies to determine whether or not changes 
within the normal range of barometric pressure 
affect activity. 
Precipitation also appears to have no effect upon 
intensity of activity, f or 35 nights during which 
0.15 or more inches of rain fell and for which 
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