of a New Hygrometer. 31 



order to discover whether my inferences would be con- 

 firmed by natural phenomena. 



Table showing the number of degrees which it is necessary 

 to subtract from the depression of temperature, produced 

 by a humid surface when exposed to a strong current of 

 air, in order to reduce the number of degrees to what the 

 hygrometer would indicate, under the same circumstances, 

 provided the atmosphere was perfectly calm. 



I shall have occasion to describe the character of the 

 Leste or dry wind of Madeira in the work already referred to ; 

 and shall there give a table, the data of which will prove 

 that this progressive increase holds good in the maximum 

 depression, I have seen the hygrometer indicate : for in- 

 stance, at 9 A. M., the hygrometer indicated 20 degrees of 

 dryness; the remarks are "quite calm, sky clear, without 

 clouds;" at 11 a.m., the hygrometer indicated 24, the re- 

 marks are " strong wind." Then on referring to the above 

 table for the necessary corrections to be made for a strong 

 wind, opposite the degree of dryness 24 will beseen4°-000, 

 which subtract from 24° =20 the degree of dryness indi- 

 cated two hours previously, when the atmosphere was calm. 

 Having proved that the depression of temperature has a 

 certain and constant limit, under given circumstances, be- 

 yond which it will not pass, I may proceed to consider the 

 second objection. 



Second objection. That evaporation takes place with greater 

 rapidity in sun-shine than in shade. The difierence in the 

 quantity of water converted into vapour in sun-shine and in 

 shade, I have not yet been able to ascertain by experiment, 



