l72r AIK BLOWN >ROM BEtLOWS. 



room. How then, Sir, are we to reconcile the refuU of 

 jour correfpondent's experiment with Dr. Black's alTerlion, 

 mentioned above? — Are we to fuppofe the blaft of air to have 

 adually acquired an increale of temperature, and if fo, how 

 has it acquired it? I hope your correfpondent (fliould this 

 ever reach his ears) will not imagine I doubt the accuracy of 

 his experiment ; my only objed is, the clearing up a cir- 

 cumftance, which at prefent is to me at leaft, not by any 

 means fatisfa61orily accounted for. To whom then can I 

 better apply, than to you, if indeed I may venture to hope 

 you may think the obje<5l worthy of your confideration ? 

 Whether tl)at fliall prove the cafe or not, I muft always fee! 

 (in common with thoufands of others) the benefit you confer 

 on the fcientilic world, by the eafy means of communicatioB 

 of knowledge to the public, which your Journal atfords, 

 I have the honour to be. 

 Sir, 

 Your obedient Servant, 



K. H. D. 



Tunbridge, 

 January 19, 1806. 



P, S, I do not underHand how the fuppofed greater capa- 

 city of a vacuum for caloric explains the fadls, whether of 

 the rife of the mercury in tl>e thermometer, or the melting o£ 

 the ice. 



Objervations on the preceding Letter, by W, N. 

 Itis deiirable WHEN a queflion arifes concerning the difagreement of 

 mentt ftould be ^^^^' ^^^ procefs obvioufly indicated is- to repeat the ex- 

 repeated, periments ; in order that it may be i^en what circumftances 

 may have tended to produce miflake, or what may have beenf 

 the real difference between operations fuppofed to be the 

 fame. Though 1 have not had an opportunity of doing this, 

 I have neverthelefs tliought it proper to make a few remarks. 

 Agitation When a body is immerfed in the air, or in any other fluid 

 tT^in the'^com. ^'^^•"'"g f'^""^ '^^^'^ '" temperature, the body will acquire 

 mon temperature the common temperature more fpeedily (that is to fay, it will be 

 morcfpcedily. heated or cooled more quickly) by agitating the fluid, than if it 

 were left undifturbed j — and this for the plain reafon, that 

 more of the particles at the original temperature will come 



into 



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