1913] COOPER—ISLE ROYALE 9 
for a partial comparison of the insular climate with that of the 
mainland. Summarization of the records for Port Arthur, Park 
Place, and Menagerie Island gives the following results: 
TABLE III 
TEMPERATURES ° C. 
June July August 
Put Arh Mean maximum 23.4 23.9 21.3 
Mean minimum 10.4 Ce ee 10.0 
Mean daily range 13.0 12.2 ax-4 
Park Places oo Mean maximum ae S14 S14 
minimum pare $254. 12.9 
Mean daily range ee 9.0 8.5 
Menagerie Island............ Mean maximum 17.0 18-8 19.4 
M inimum Hie 10.5 23:5 
Mean daily range 9.9 8.3 6.3 
From this table we see that the maxima upon Isle Royale 
are lower than upon the mainland, during the summer at least. 
Menagerie Island, most under the lake’s influence, is the lowest, 
and Park Place, upon the main island, is intermediate. We may 
infer that as a result of lower temperatures the evaporation is less 
upon Isle Royale. Apams (4, p. 44) suggests that insular location 
and imperfect drainage probably operate to reduce evaporation. 
The table also shows that the Isle Royale climate is characterized 
by less pronounced daily temperature changes than is that of the 
mainland. The daily range is shown to be uniformly greatest at 
Port Arthur, intermediate at Park Place, and least at Menagerie 
Island. 
A further comparison (table IV) brings out the fact that the 
proximity of the lake retards the opening of the growing season, but 
also that the same factor prolongs it into the fall. : 
TABLE IV 
MEAN MONTHLY TEMPERATURES (° C.) May-Nov.; AVERAGE 1906-1909 
May June July | August} Sept. Oct. Nov. 
PORt ATU oe i 4s 6 1 10.8) £8.05) 41.6 1.28.7 ie. 
Menagene Isiang.. 2.22... A:3 1 8.0 1 11.6 | 34.8 1.52:5 |. 6.8) 3.0 
