25-percent reduction in activity with a 22 degree 
drop in temperature. This decrease in actual 
intensity of activity accompanying the decrease in 
temperature was nearly as much (25 percent 
instead of 33 percent) as might have been antici- 
pated on the basis of the analysis of the relative 
change in activity between pairs of days. 
The influence of barometric pressure upon activ- 
ity, independent from that exerted by temperature, 
is difficult to determine because there is generally 
an inverse relationship between the direction of 
changes of these two factors. In examining the 
meteorological records for individual days it was 
noted that there were certain nights during which 
barometric pressure continuously decreased where- 
as on other nights it continuously increased. By 
comparing the mean change in meteorological 
conditions on these days with the mean activity 
rhythms on the same group of days, the character 
of a possible influence of barometric pressure upon 
activity should be revealed. These calculations 
are shown in figures 100 and 101. For the six 
pairs of nights during which the temperature was 
above 55° F. there is no apparent differences in the 
activity rhythms. In fact, the pre- and post- 
midnight activity was nearly identical despite 
the marked difference in pre- and post-midnight 
barometric pressure on these days. Nor is there 
any evidence from the more extensive series of 
data when the mean nightly tenperature was below 
55° F. that barometric pressure affects intensity 
of activity. There is only a slightly greater slump 
55°F. ( 6 PAIRS OF DAYS ) 
55° F. ( 20 PAIRS OF DAYS ) 
Figure 100. — Nocturnal changes in temperature and barometric pressure. Nights having continuously rising barometric 
pressure are compared with those having continuously falling barometric pressure. In either case there is a drop in 
temperature from 6 p.m. to 6 a.m. However, note that the drop is much greater on nights of rising barometric pressure. 
129 
