CHEMICAL AND PHYSICAL NOTES, 145 
Example of the Method of Determining the Calorifie Power of the 
Sun’s Rays, which strike the bulb of a Thermometer and are absorbed 
by it ; and of the difference between different thermometers in this respect. 
—The following observations were made with two thermometers of 
very different pattern, They were hung side by side in a room 
exposed to the powerful winter sun at St. Moritz, in the Engadine, 
between 11 and 11.30 a.m. on February 26,1901. The thermometers 
are designated A and B. A is an ordinary German thermometer, 
divided into whole degrees on a milk-glass scale and its bulb was 
coated with silver. B was an English thermometer with solid stem, 
and divided into tenths of a Centigrade degree, each degree occupying 
a length of lcm. Its bulb was not coated in any way. The par- 
ticulars relating to the bulbs were obtained by mensuration as above 
described. The mean altitude of the sun was 33° and cos 33°= 0°84; 
the axial sectional area of each thermometer has to be multiplied 
by this factor in order to obtain the effective area exposed, or rather 
to obtain the sectional area of the bundle of rays which strikes the 
bulb of each thermometer. 
Taste XVIIL—Specirication oF ‘tHe THERMOMETER. 
Designation of thermometer ‘ : j A B 
Diameter of bulb .. moe 45 em. | a | 0°637 | 0°471 
Length of equivalent cylinder . em. | b 2°3 2-4 
Volume of bulb . ‘ - : ce. | € | 0°7334 | 0°4181 
Water value of bulb . . grms. | d | 0°3375 | 0:1923 
Area of external surface com.? | e 4°92 3°727 
Area of axial section. ato oo. . em? | f | 19465 | 1-130 
Effective area of ditto ‘ - em? | g | 1°230 | 0°950 
Term of cooling 3: fs seconds | h 250 120 
In Table XVIII. we have the specifications of the bulbs of the 
thermometers. It will be observed that the “length of the equiva- 
lent cylinder” 6 is given simply, in place of the cylinder and two 
hemispheres, as in the case of thermometers with large bulbs. The 
volume of the bulb ¢ is found by multiplying the circular area corre- 
sponding to the diameter a by the length of the equivalent cylinder b. 
The water value of the bulb is d= 0°457c. When this table was 
calculated, 0°457 was used as the specific heat per unit volume of 
the bulb, instead of 0:475, which was adopted later. It has not 
been thought necessary to recalculate the table. The area of external 
surface is the circular area of the diameter, added to the product of 
the length of the equivalent cylinder and its circumference. The 
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