METEOROLOGY AND ALLIED SUBJECTS. 



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the radiation. Ab soon as dew begins to form this condensation now 

 acts in a direction contrary to that of the previous evaporation ; by this 

 condensation the latent heat of the aqueous vapor is set free, and so 

 delays the further process of cooling through radiation. 



This superposition of the two processes can be best investigated if 

 we endeavor to observe them separately. Take three thermometers — 

 the first having a metallic polished spherical bulb, the second a dry 

 blackened spherical bulb, the third a wet or moistened blackened spher- 

 ical bulb. Then the first thermometer, if it is protected from the heat 

 radiated from the earth, and also protected by a roof, will give simply 

 the temperature of the air, since the radiating power of its own surface 

 can be taken as zero; the second thermometer, if allowed to radiate 

 freely into the sky, 'will give simply the efiect of radiation; the third 

 thermometer, also radiating freely to the sky, will give the total effect 

 of radiation and evaporation together. Such investigations, according 

 to, Jamin, show that the cooling due to evaporation is almost always 

 equal to that due to radiation, and sometimes exceeds it ; therefore, in 

 the explanation of the forming of dew it is certainly not to be neglected. 

 The following example of observed temperatures, before and after the 

 formatien of dew, sets the whole process forth more clearly : 



' Dew point, 7.05. 



{Z. 0. O. 3L, XIV, p. 324.) 



In a short article on the climate of central equatorial parts of the 

 Pacific Ocean, Woeikof collects together a few notes relative to obser- 

 vations made on small guano islands near the equator. He especially 

 calls attention to the small rainfall recorded for these islands, and 

 suggests that durable rain gauges be constructed of such pattern that 

 they can be permanently left on such small uninhabited islands, and 

 from time to time be visited in order to keep the record of the rainfall. 

 He expresses the hope that navigators of the Navy or merchant marine 

 may find opportunity to carry out his suggestion. {Z. 0. 0. M., XV, 18S0, 

 p. 120.) 



In a note on crystallized forms of hail, Merrian states that among the 

 various views that have been expressed as to the origin of these forms, 

 it seems to him probable that repeated melting and freezing of layers 

 of water plays an important part. We can assume that at first a kernel 



