234 Annals Entomological Society of America [Vol. VIII, 
F. Seasonal Changes. The general weather conditions 
for 1913 are expressed in the following chart: 
H. WEATHER CONDITIONS, CANAL ZONE, 1913. 
Rainfall deficient (except Brazos Brook, Colon and Porto Bello). 
Dry season rainfall: 
Pacific section=4% total. 
Central section=6% total. 
Atlantic section=10% total. 
March least rain. May most rain. 
Air*temperature and wind movement slightly above normal. 
Atmospheric pressure and cloudiness generally deficient. 
ey ial 
B Temperature ie | Precipitation Wind Movement 
od se | | 
rs ] es ~ aD) > a2) a - 
Gs) | le B : o Palicon=ees pa = S 
| 29s || O-5 rs} 0 i153 0 M|.4.2/O e} 
ect eter) Shell ps BS lS cISeelesleal S 
a —_ a= fe} | CT ae] aot (S) 
\eeeisi/e| 2 || 2 88) 8 | Se lssleselasigel 2) 8 
AS ry -_ I | a ol! ~— ~— _ 
) ae Je a Wai Taak er ah ena co ayo) st tl = Wie) frie 
7 i \| | | 
Colon...| 29.866 |80.1) 91 | Jun. 22 | 71 | Feb. 4/| 85 || 131.22 | 129.38 246, 1 N | 36 | N | Nov.14 
=) 
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0.7 
Culebra, 29.846 |79.2) 95 | Apr.14 | 64 | Jan. 4 : i | 7.3 |NW| 40 |NE| Nov.19 
Ancon..| 29.834 |80.3] 96 | Apr.27 | 66 | Feb.22 || 87 || 65.98 | 70.90 | 180)} 7.2 |NW| 32] S | Jun. 11 
| 
At a given station, seasonal variation is not marked. But 
it is evident that at Ancon, where rainy days are one third less 
than at Colon, and rainfall less than one-half, that a different 
set of conditions are present there than at Colon. 
It is interesting to note that the rainfall for December ’12, 
was generally deficient throughout the Zone, but that at the 
Colon-Gatun section it was much heavier. Thus the swamp 
near Gatun which caused so much Anopheles breeding in the 
early part of 1913, was prepared for such wide-spread breeding 
by this increased rain. The influx of pure water meant that 
the salts in the swamp, which rapid evaporation was about to 
make stronger, were kept diluted and never became so strong 
as to inhibit mosquito breeding. It meant also that the density 
of the water was lowered. 
In January, 1913, temperature and relative humidity were 
above the average. February continued with deficient wind 
movement. March and April showed also a deficiency in 
relative humidity and atmospheric pressure. In May these 
conditions reached their normal. Cloudiness had been deficient 
throughout the dry season. 
