C 417 ] 



LXXVL 0?i the supposed Dlmimition qf Volume which IVater 

 at 32" undergoes by Jdditiom of Tempiiiature till it reaches 



41°. By A CoURI'SPONDENT. 



To Mr. rUlocL 



Sir, — i RKVfous to tlve 'adnii-sion nf a fact which is a re- 

 inarka!)]e exception to a known law of nature, it ought to be 

 estabhshcd by the most direct and decisive experiments ; and it 

 ought to serve some inVportant purpose in the oeconomy of na- 

 ture whicii could not be accomplished by any other n)eans ; 

 otherwise, such a deviation from a general law would not be 

 consistent with the dignity of an infinitely wise Creator. 



It apperirs to be a general law of nature, that all bodies are 

 expanded l)v licat: water, at low temperatures, is said to be an 

 exception: the following- are supposed to be the phaenomena. ^ 



When heat is added to water ice-cold or at 32°, the water 

 contracts, and continues to contract as heat is added til! its tem- 

 perature is increased to 41'^': then, without any perceptible alte- 

 ration in its ])roperties, the water begins to expand, and increases 

 in volume with every su!)sequent ad<lition of heat. 



Mr. Daiton, after a long train of experiments, was led to be- 

 lieve that lie, and liis predecessors in the same field of investiga- 

 tion, had fallen into a mistake with regard to the contraction of 

 water by heat, in consequence of under-rating the effect which 

 the change in the capacity of the apparatus employed must oc« 

 tasion in the apparent volume of the fluid. 



To remove this objection, to which all the preceding ex- 

 periments were liable, Dr. Mope made a new set of experiments; 

 in which, we think, there is more confidence ])laccd than the 

 nature of the experiments entitles them to. The principle on 

 which these experiments were made, is, that when a fluid is 

 partially dikitcd or condensed the equilibrium is destroyed, and 

 the fluid })ut in motion: consequently, if the surface of ice-cold 

 water when heated descends, it shows that heat condenses water, 

 and proves the existence of the anomaly, and the reverse if it 

 does not descend. 



It must be obvious that the manner in which the lieat is com- 

 municated will make a very great difference in the results. la 

 the first of Dr. Hope's experiments (Piiil. Mag. vol. xxiii. 

 p. 1j."5), a glass jnr was used: it was placed upon a table, with a 

 considerable thickner,s of matter of little conducting power be- 

 tween it and the table. Now the worst solid conductor will com- 

 municate heat much better than a fluid ; and glass, interposed 

 between two fluids, transmits heat very slowly till it acquires the 

 temperature of the fluid giving out heat: hence the greater part 



Vol. 1(1. No. 212, Dn. l8l j. D d of 



