128 APPENDIX. 



Defcriptlon of the Manometer, conftrufled by Mr. 



Ramfden. 



The Manometer ufed in this voyage was compofed of 

 a tube of a fmall bore, with a ball at the end ; the baro- 

 meter being at 29,7, a fmall quantity of quickhlver was 

 put into the tube to take off the communication between 

 the external air, and that confined in the ball and the part 

 of the tube below this quickfilver. A fcale is placed on 

 the fide of the tube, which marks the degrees of dilata- 

 tion arifmg from the increafe of heat in this flate of the 

 weight of the air, and has the fame graduation as that of 

 Fahrenheit's thermometer, the point of freezing being 

 marked 32. In this flate therefore it will (liew the 

 desfrees of heat in the fame manner as a thermometer. 

 But if the air becomes lighter, the bubble inclofed in the 

 ball, being lefs comprefled, will dilate itfelf, and take up a 

 fpace as much larger, as the compreffing force is lefs ; 

 therefore the changes arlfing from the increafe of heat will 

 be proportionably larger; and the inftrument will fliew 

 the differences in the denfity of the air, arlfing from the 

 changes in its weight and heat. Mr. Ramfden found, that 

 a heat, equal to that of boiling water, increafed the mag- 

 nitude of the air from what it was at the freezing 

 point -,*-^%^ of the whole. From this it follows, that the 

 ball and the part of the tube below the beginning of the 



fcale 



