ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 205 



Maxima, hourly horizontal movement more than 15 miles. 



Period. 



November, 1872 (no calnis) 



January, 1873 (37 calm hours) 



February and Marcb, 1876 (no calm hours) . 

 January and February, 1877 (17 calm hours) 



November, 1877 (no calms) 



January, 1878 (24 calm hour*) 



November and December, 1880 



November, 1881 



November, 1882 



January, February, and March, 1883 



November and December, 1883 



January and February, 1884 



December, 1884 



February, 1885 



December, 1886 



February and March, 1888 



February, 1889 



January, 1890 



Total 



Death 

 rate. 



Death rate 



in live 

 weeks fol- 

 lowing. 



22.8 





24.5 



19.2 





24. 8 



24.6 





23.4 



21. G 





27.6 







25.3 



26. G 





25.4 



21.9 





25.0 



21. 18 





23.1 



21.26 





23.5 



21.9 





23.6 



21.23 





20.4 



21.22 





19.9 



21.6 





23.2 



19.6 





22. 



20. 9 





21.8 



21.2 





19.0 



18.2 





18.6 



28.1 





21.4 



22. 15 



23.1 



DEW AND FROST — EXHALATION OF VAPOR FROM THE EARTH. 



From an investigation conducted by the present writer during the 

 two summers 1891 and 1892, the following were among the conclusions 

 arrived at: 



Calm or a light air is favorable to dew formation. Wind prevents 

 the deposition of much dew and evaporates much of what is formed. 

 Free radiation or an exposed situation is, on the whole, perhaps the 

 most effectual cause of dew on very many nights of the year. In a 

 level country those parts of a field which are least sheltered by trees 

 and hedges gain most dew on perfectly calm nights. Those parts of 

 any flat substance with the most exposure to the sky are on calm nights 

 most bedewed. The tops of bushes, posts, railiugs, pans, etc., are on 

 calm nights more bedewed than the sides. Greater cold by greater 

 radiation in these cases produces greater deposition. Radiation from 

 fine points, however, is often not sufficient to counteract in air which is 

 not very humid the effect of the continual impact of air above the dew- 

 point and higher in temperature. Close to the ground the case is gen- 

 erally different, for the movement of air is less and the humidity and 

 cold greater. With fog or a very humid air the points are most bedewed. 

 In dry weather the dew is deposited most on the leeward side, in moist 

 air or fog on the windward side of objects. 



Nearly all the conclusions of Wells were confirmed. But a very 

 remarkable amount of evidence soon accumulated from the experiments 

 that a great proportion of the dew formed near the ground is condensed 



