a 
EE —— <r 
209 
composed of louvre-boards, like Venetian shutters, by which is insured a free 
circulation of air through it, while the direct influence of the sun upon the 
interior is excluded. Below the louvre-boards the sides are simply covered with 
iron network—a precaution necessary to prevent interference with the instru- 
ments. Within the building is a framework to which the thermometers are 
fixed, likewise closed at the top andon three sides, but open to the North 
(where the door of the building is), witha space of fifteen inches between the 
back and the outer casing, affording still further security against the influence 
of the heating power of the sun’s rays.” 
“The thermometers, which are so placed as to have their bulbs about four 
feet from the ground, consist of two self-registering ones, for day and night 
respectively, and a dry-and wet-bulb. They were made by Negretti and 
Zambra, and compared by Mr. Glaisher with standards at the Greenwich Obser- 
vatory before being sent. The necessary corrections for instrumental error are 
applied each time the observations are made. In addition to the thermometers 
is a Rain Gauge,—fixed at the top of the building, at the height of eight feet 
from the ground,—consisting of a copper funnel, the mouth six inches in 
diameter, with a vessel beneath capable of holding a gallon or more, to the 
bottom of which is attached a stop-cock, by means of which the rain is drawn 
off and measured in a graduated cylindrical glass jar: of these glasses there 
are two, one divided into hundredths of an inch, the other of less diameter into 
thousandths for small quantities of rain.” The estimated height of the Rain 
Gauge, above the sea, is seventy-five feet. 
The observations are registered every day at 9 a.m. local time. 
The maximum and minimum temperatures entered in the register 
are the highest and lowest that have occurred during the previous 
24 hours. The quantity of rain entered is the amount fallen 
during the same interval. 
The Registration of the Thermometers and Rain-gauge com- 
menced on March Ist; 1865,—but that of the wet-and dry-bulb 
not till the 14th June following ;—and the remarks that I shall 
have to make in this paper principally relate to the results 
obtained by these instruments during ten years dating from the 
day above-mentioned. A shorter period than ten years would 
have been insufficient for the deduction of averages that could be 
at all relied upon ;—while a much longer term of years I conceive 
is yet wanted to make the averages thoroughly correct,—especially 
