at Sierra Leone, by Captain Sabine. 71 



upper and lower barometer, under equal pressure, was in all 

 cases carefully examined, and the difference, if any, allowed as 

 an index error to the lower barometer. I have great pleasure 

 in remarking, that I found much less difficulty than I had an- 

 ticipated, in getting corresponding observations made with the 

 hygrometer, on the correctness of which I could sufficiently 

 depend; the ingenuity in the principle of this instrument, and 

 the simplicity of its application, together with the decisive na- 

 ture of the results which it gives, independent of the labour, and 

 at best, the uncertainty of formulaic deduction, form its great 

 advantage over the methods by evaporation, or the indications 

 of hygroscopic substances: these particulars excite an interest in 

 its trial in persons to whom it was previously unknown, which is 

 probably the reason that the distrust, which is almost always 

 in the first instance expressed of precision in the observation 

 itself, is found to give way in practice so much sooner than 

 might be supposed. It may be useful, also, to travellers in warm 

 climates, to add a remark from my own experience, that in as- 

 cending elevations, or in journeying inland over rough roads, 

 the ether carries perfectly Avell in a bottle in the waistcoat 

 pocket, with a common cork capped with leather; and that the 

 expenditure of ether altogether will probably fall much short 

 of the estimate, as, with ordinary care, vcy little will be 



wasted. 



Believe me, my dear Sir, 



Very sincerely yours, 



Edward Sabixe. 

 London, March 17, 1823. 



Art. X. On Hydrate of Chlorine. By M. Faraday, 

 Chemical Assistant in the Royal Institution. 



It was generally considered before the year 1810, that chlo- 

 rine gas was condensible by cold into a solid state ; and we 

 were first instructed by Sir Humphry Davy, in his admirable 

 researches into the nature of that substance, published in the 

 Philosophical Transactions for 1810-11, that the solid body, 

 obtained by cooling chlorine gas, was a compound with water ; 



