FARM SANITATION 



507 



time to kill them, while some intestinal bacteria were killed 

 in a few hours. It was also found that bacteria are killed 

 more quickly in moist air than in dry, contrary to general 

 belief. The diffuse light as found in our dwellings is, there- 

 fore, a hygienic factor of great importance, and where direct 

 sunlight is not available it should be carefully provided for." 

 It is believed that the above quotation represents a clear, 

 authoritative statement of the value of diffuse sunlight in 

 producing sanitary quarters. 



Location of Windows. In locating the windows, great 

 care should be taken that sun- 

 light will be admitted in such 

 a way as to allow the direct 

 beams of light to sweep the 

 entire floor. The angle of 

 incidence of the sun's rays, or 

 the distance of the sun above 

 the horizon, for latitude 42° 

 north varies from 70° the 22nd 

 of June to 26° the 21st of Dec- 

 ember. For other latitudes 

 the angle of incidence is 

 different. At the spring and 

 fall equinoxes, which take 

 place March 21 and Sept- 

 ember 21, and for 42° N. the 

 angle is 48°. Sunlight is more 

 useful in the winter time than 

 in the summer, and care 

 should be taken to make use of the winter sun rather than the 

 summer sun. For practical purposes it can be assumed that 

 the most desirable sunlight enters the windows at an angle 

 of 45°. 



Fig. 311. A sketch showing how 

 the angle of incidence of the sun's 

 rays varies throughout the year. This 

 is at latitude 42° N. 



