IXTRODUCTION". 67 



log. OS8 =z o 37G58 X -^ = 4J5310 

 log. 230 = 2,39794. X -^ = 4,79588 



log. sill. 1 = 9,95728. I = 65° 0' 

 Among the general observations, which are no 

 less imjDortant to nautical than to physical science, 

 may be especially reckoned the investigations of 

 the atmosphere, with respect to its weight and 

 temperature ; the very great simplicity, precision, 

 and commodiousness of the two instruments re- 

 quired for this purpose, the barometer and tlie 

 thermometer, render them perfectly adapted to be 

 used by sea, and the observations made by their 

 means, serve the attentive seaman to fbretel the 

 weather, besides furnishing the meteorologer and 

 natural philosopher with a closer acquaintance 

 with the course of the changes of the weather in 

 general, and with the properties of the atmo- 

 sphere depending on geograpliical position. 



With respect to the barometer, the observation of 

 it is much facilitated by hanging it judiciously, 

 and lessening the motion of the quicksilver. Yet 

 it requires considerable practice to recognize its 

 real height. It is not sufficient to observe only 

 the maxima and minima of the oscillations of the 

 mercury, but one must often stand for minutes 

 together before the barometer, in order to catch a 

 moment, when the irrational oscillations of the 

 ship and of the instrument, mutually destroy each 

 other, and the mercury becomes, for a moment, 



F 2 



