REGNAULT'S HYGROMETER, WITH ASPIRATOR. 



These instruments consist of a thin and highly- 

 polished tubular vessel of silver, having one end 

 somewhat longer than the other. A very delicate 

 thermometer is introduced into the tube at the 

 smaller end, to which end of the tubular vessel, 

 also, a flexible rubber tube with ivory mouth- 

 piece is attached. A sufficient quantity of ether 

 to cover the bulb of the thermometer, being 

 poured into the silver vessel, the ether is agitated 

 by breathing through the flexible tube. A rapid 

 evaporation ensues until at the moment the dew- 

 point is reached, the moisture is seen to condense 

 upon the exterior surface of the polished silver 

 tube. The reading of the thermometer at this 

 precise moment gives the dew-peint. Complete in 

 case, $75.00. Too high priced for ordinary use, 

 but a splendid addition to an experimental outfit. 

 130 



