GRISCOM ON METEOROLOGICAL OBSERVATIONS. 347 



means of improving the theory of evaporation and condensation. Hy- 

 grometers of different kinds, and depending on different principles, have 

 been employed for this purpose. That contrived by Lieutenant Kater 

 we have ascertained to be very sensible in its operation. Professor 

 Leslie, of Edinburgh, has invented several instruments for this purpose, 

 which have simplicity and facility of management to recommend them. 

 They are particularly described in his late work on the " Relations of 

 Air to Heat and Moisture." It is well known that in warm weather a 

 common drinking glass is a good hygrometer; for when the internal 

 surface is refrigerated by pouring in a cold fluid, the moisture which 

 condenses externally, affords an indication of the quantity existing in 

 the atmosphere, which, when excessive, is considered by many as pre- 

 saging a change of weather. Such indications, when remarkable, are 

 worthy of being registered by the daily observer; and we would recom- 

 mend that the person appointed to keep the meteoric register should 

 be instructed to note the state of the hygrometer. 



Before a correct, or, at least, a complete, theory of the weather can 

 be arrived at, it will, in all probability, be requisite that greater advances 

 be made in our knowledge of the electrical changes that take place in 

 the atmosphere during the transitions from heat to cold, from foul to 

 fair, and the contrary. To ascertain this point effectually is no easy 

 task. It will require great patience and assiduity of attention. But 

 though an extensive course of electrical observations, persevered in for a 

 long time, might prove too laborious, it would still be desirable to note 

 the observance of those changes which occur in all the most remarkable 

 revolutions of the elements. This could be done by means of an insu- 

 lated spire, or an electrical kite, or, with still greater facility and cheap- 

 ness, though less effectually, by the atmospherical electrometer of Saus- 

 sure, or the more simple instrument of Cavallo. We have observed 

 remarks of this nature in some of the meteorological journals of Europe, 



