346 GRISCOM ON METEOROLOGICAL OBSERVATIONS. 



exposed circumference of the instrument, and to melt it without any 

 loss by evaporation. 



4th. Changes in the direction and force of the wind. 



In order to ascertain the quarter from whence the wind blows, any of 

 the city vanes which are known to turn easily, and which are within 

 the reach of the observer's eye, may, perhaps, be sufficient. It would, 

 however, in our opinion, be desirable that an instrument combining the 

 properties of an anemoscope with those of an anemometer, which de- 

 termines the relative force and velocity of the wind, should be provided 

 as soon as the funds of the society will justify a little expenditure for 

 this purpose. Various instruments have been contrived for measuring 

 the force of wind; but we believe the one invented by the celebrated 

 Kir wan is by far the most complete. It is described in the transactions 

 of the Irish Academy, and in the 34th volume of Tilloch's Philoso- 

 phical Magazine. By this the strength of the wind, from a gentle 

 breeze to the most violent hurricane, may be exactly measured. 



The subjects now enumerated, are considered essential in every 

 course of meteorological observations, which has the ordinary aim 

 either of curiosity or information. But to render such a series com- 

 plete ; to make a collection of facts that may be held up as an example, 

 and serve as the basis of useful induction to those who shall come after 

 us, there are various other phenomena which, we think, ought not, on 

 an occasion of this nature, to be neglected. The committee hope not 

 to trespass beyond the proper limits of their duty in attempting a brief 

 detail of those which they consider the most important. 



The relative quantity of moisture contained in the atmosphere at 

 any given period, is an object, the knowledge of which is desirable not 

 only for the purpose of comparison, but in an especial manner as the 



