THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



AUGUST 1854. 



XL On a new Hygrometer or Dew-point Instrument. By A. 

 CoNNELL, F.R.S.E., Professor of Clbemislry in the University 

 of St. Andrews^. 



[With a Plate.] 



THIS instrument, like Professor DanielPs, produces the cool- 

 ing effect on the surface which is to exhibit the deposition 

 of dew, by the evaporation of aether ; but it differs from it entirely 

 as regards the manner of producing that evaporation. It is in 

 no respect a cryophorus, but causes and maintains the evapora- 

 tion simply by the action of a small exhausting syringe. The 

 accompanying figure (Plate I. fig. 3) will explain the nature of 

 the arrangement. 



A is a little round bottle of thin brass, well polished on the 

 outside, and capable of holding, when filled to the bottom of its 

 neck, half an ounce of liquid. Its diameter is about I/^ths of 

 an inch. Its neck is f inch high and about j\ inch wide, and 

 spread out a little at top. The passage M which conducts into 

 the neck has throughout an internal diameter of |- inch, and 

 it is very essential that it should not be narrower than this. 



B is a small mercurial thermometer, the bulb of which reaches 

 within ^th of an inch of the bottom of the bottle, and the uppter 

 part of the bulb is on a level with the surface of the liquid 

 contained in the bottle, or a little above that level. The bulb 

 should not be entirely immersed in the liquid. It is an 

 elongated cylinder about f rds of an inch long by about ^th 

 of an inch in diameter. This thermometer has a small scale 

 attached to it, graduated according to both Fahrenheit and Cel- 

 sius' scale from 0° F. to 100° F. The stem of the thermometer 



* Abridged from a Memoir read to the Royal Society of Edinbm-gh on 

 the 3rd of April, 1 854, and to be published in their Transactions, vol. xxi. 

 Phil. Mag. S. 4. Vol. 8. No. 50. Aug. 1854. G 



