Dr. Apjohn /« reply to Dr. Hudson. 187 



wide ocean, if we ever possess the power; but when it is ac- 

 complished we can hardly yet tell to what discoveries it may 

 lead. We may, probably, be enabled to calculate the gradual 

 approach of what will be hereafter new continents and islands, 

 and to trace the boundaries of those which have once existed ; 

 or we may discover in deep chasms and ranges of submarine 

 mountains the causes of those currents which, in spite of the 

 assistance of modern astronomy, are still occasionally so dan- 

 gerous to the navigator. At all events it must be interesting 

 to unveil the secrets of the abjss, no longer unfathomable, and 

 to send our inanimate messengers to bring us the intelligence, 

 and possibly some of the productions, of those regions where 

 neither the eye of man nor the light of heaven has yet been 

 able to penetrate. J. J. 



X L. On certain Statements relative to Dr. Apjohn's Hygro- 

 metrical Researches contained in Dr. Hudson's Papers in- 

 serted in Lond. and Edinb. Phil. Mag., vol. vii. and vol. viii. 

 % James Apjohn, M.D., M.R.I.A., Professor of Che- 

 mistry in the Royal College of Surgeons, Ireland. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 FN a paper by Dr. Hudson of this city, published in the 

 Philosophical Magazine for October 1835, there are some 

 statements relating to certain hygrometrical researches of 

 mine which, though it be contrary to my original intention, 

 I find myself, eventually, in some degree compelled to notice 

 and contradict, and with this view have to request that you 

 will give an early insertion in your Journal to the following 

 brief detail of facts. 



In November 1834, I had the honour of reading a memoir 

 to the Royal Irish Academy, an abstract of which was pub- 

 lished in the Number of the Philosophical Magazine for the 

 following March. In this was investigated and explained the 

 following expression, which includes the ^solution of the well- 

 known dew-point problem : 



•' -^ 87 30 • 



Dr. Hudson, who was present at the reading of this paper, 



• d is tlie difference of tlie temperature shown by a wet and dry ther- 

 mometer, f the force of va()oiir at the ten)[)craturc indicated by the 

 former, and /" its force at the dcujiuiut. 



X2 



