abftraiSling from the influence of vapour. If the defcent of the 

 hygrometer be fuch as the table (hews to refult from the mere in- 

 creafe of heat, then there was no increafe or decreafe of vapour ; 

 but if the defcent ht fmalkr than mere heat would occafion, then 

 there muft have been an increafe of vapour ; and if the defcent be 

 greater^ then there muft have been alfo a decreafe of vapour as well 

 as an increafe of heat. 



Tntjs, I *'.'Suppofe an hygrometer to ftand at XCVIII, at any 

 given degree of heat, and that the heat afterwards increafes 5° of 

 Reaumur, and then that the hygrometer ftands at LXXXIV and 

 four-tenths, and it is required to know to what caufe this afcent is 

 to be attributed. 



Remark, in the firft obfervation, at what thermometrical dif- 

 tance XCVIII ftands from C, that is, what degree of cold or de- 

 creafe of heat it wants to bring it to C. Now in the fecond 

 column of this table you will find i',399 oppofite to, and corref- 

 ponding with XCVIII, therefore it wants i*,399 degrees of Reau- 

 mur to bring it to C. But if the heat be increafed five degrees 

 more, then it is plain it will want 6,399 degrees of cold to bring 

 it to C. Look then in the fecond column of the table for this 

 number ; you will not find it exadly, but you will find it is inter- 

 mediate between the tabular numbers 6,182 and 6,561, but nearer 



3 R a to 



