Daniell oti n new Tli/grometer. 321 



peared, and the gauge stood at 24.2. No precipitation took 

 place at a temperature of 34° ; the air was gradually re-admitted, 

 and the deposition took place with the hygrometer at 36°, and 

 the gauge at 15° *. 



Exp. 4. The receiver was tilled with o.xygen, in contact with 

 water, and afterwards with hydrogen ; but the point of con- 

 densation was the same as when tilled with common air, under 

 the same circumstances. This, and Experiment 2, fully coincide 

 with Mrj Dalton's view of the theory of mixed elastic fluids, 

 and prove, indeed, that the gases are ds vacua with regard to 

 vapour ; and that, where they happen to be mixed together, they 

 exist as independent atmospheres. 



Exp. 5. Having absorbed all the vapour contained in the 

 receiver, by means of sulphuric acid, I placed it over some 

 spirits of wine. After remaining some hours in this situation, a 

 fevf drops of ether upon the external ball produced an instant 

 condensation upon the internal one. The experiment was re- 

 peated with ether in the place of the spirits of wine, with the 

 same results. 



Exp. 6. The temperature of a room being 45°, I found the 

 point of condensation in it to be 39°. A fire was lighted, the 

 door and windows carefully shut, and no one allowed to enter. 

 The thremometer rose to 55°, but the point of condensation re- 

 mained the same. A party of eight persons afterwards occu- 

 pied the room for several hours, and the fire was kept up. The 

 temperature increased to 58°, and the point of condensation 

 rose to 52°. 



Exp. 7. Being desirous of ascertaining, as perfectly as cir- 

 cumstances would allow, the effect of height, as regarding the 

 vapour in the atmosphere, I made a series of observations in 

 the exterior iron gallery of St. Paul's, in diflferent states of the 

 weather, of which the following are the results. They are ar- 

 ranged for convenience in the tabular form. 



* In lielicalc experiments of this kind, a lighted tiipcr in a glass lantern 

 placet! behind tlifi bnib of the instrnmeiit, renders the deposition more 

 easily visible, and ensure* ntcurary. 



