48 “THE HABITAT 
These may be combined in a series for the comparison of readings made at 
various heights in the stations. The day or point curve shows the fluctuations 
during the day of one point, and the station curve the variation at different 
heights in the same station. The curves of successive days or of different 
stations may of course be combined on the same sheet for comparison. Level 
‘and station curves based upon mean relative humidities are especially 
valuable. 
75. Records. A field form is obviously unnecessary for the psychrograph. 
The record sheets constitute both a field and permanent record. The alti- 
tude and other constant features of the station and the list of species, etc., 
are entered on the back of the first record sheet, or, better, they are noted 
in the permanent formation record. For psychrometer readings, whether 
-single or in series, the following record form is employed: 
ee ta lo il/gig NOTES 
P 3 2 4 Swis/2) |e) 8) § 
7 3 2 g 65/0/48 ala] a 3 
2| es] i | 2 | 2 | se [eeelsels/sla|o lai 
A = Ze ii < 68. Peale ls)a/a] <4] a | a |e 
15/8/'04'6:20a.m.|Spruce ....] Brook bank] 2500 m | Mertensiare|1 ft. 519/46° 5| 72%) 634) 2.9)Clear| 0 | 0 
a we Half gravel] Hiawatha .. ee Asterare ...| ‘ |56°}49°] 7) 64%] 63%) 3.0) ‘‘ 0/0 
ae 6:45 P M./Spruce .... Brook bank| Mertensiare| *' /54°/52°) 2) 89%) 69%) 4.2} ‘* |2cc.| 0 
a ee _|Half gravel} Hiawatha .. ne Asterare*~..| ‘* |56°|52°) 4) 79%! 69%] 4.0} ‘‘ |2cc.] 0 
On page 47 is given a table for the conversion of Centigrade into Fahren- 
heit temperatures. This may be done mentally by means of the formula 
C 
F=— X9+32°. 
LIGHT 
76. Methods. Atl methods for measuring light intensity, which have been 
at all satisfactory, arc based upon the fact that silver salts blacken in the light. 
The first photographic method was proposed by Bunsen and Roscoe in 1862; 
this has been taken up by Wiesner and variously modified. After consider- 
able experiment by the writer, however, it seemed desirable to abandon all 
methods which require the use of “normal paper” and “normal black” and to 
develop 2 simpler one. As space is lacking for a satisfactory discussion of 
the Bunsen-Roscoe-Wiesner methods, the reader is referred to the works 
cited below. Simple photometers for making light readings simultaneously 
1BunsEN, R., AND RoscoE, H. Photometrische Untersuchungen. Poggendorff’s 
Annalen., 117:529. 1862. 
WIESNER, J. 
Photometrische Untersuchungen auf pflanzenphysiologischen Gebiete. Sitzb. Akad. 
Wiss. Wien., I, 1893. II, 1895. 
