96 



Chemical and Physical Notes 



amongst common thermometers of the same pattern, which 

 are turned out in large quantities at a time. 



Example of the Method of Determining the Calorific 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 thermo- 

 meter, 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 I cm. 

 Its bulb was not coated in any way. The particulars 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. 



TABLE XVI. Specifications of the Thermometers. 



In Table XVI we have the specifications of the bulbs of 

 the thermometers. It will be observed that the " length of the 

 equivalent cylinder" b 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 c is found by multiplying 



