244 DR HOPE ON THE MAXIMUM DENSITY OF SEA-WATER. 



cold, than to depress the point at which that quality begins to be sensible, just as 

 much as it depresses the point of congelation." 



Sir Charles does not describe the apparatus which he employed ; he only 

 says that he introduced the solution of salt into an appai-atus he had used for 

 other experiments of the same kind. I have no doubt the apparatus was a vessel 

 of glass, having a comparatively slender neck, in which small variations in bulk 

 of the contained fluid could be easily discerned, analogous to that originally em- 

 ployed by Dr Crone in 1688 to demonstrate the expansion of water as it ap- 

 proaches the freezing point. 



It is familiarly known, that when water at temperature 50°, included in such 

 an apparatus, is exposed to cold, it descends in the stem till its temperature 

 reaches the 41°, and continues nearly stationary while the temperature falls to 

 39^° ; but when the temperature of the fluid declines below that point, the water 

 begins to rise in the stem, and continues to do so as the temperature sinks to 

 the 32°. 



From the detail of Sir Charles above quoted, it appears that, having intro- 

 duced a solution of common salt, in the proportion of 4.8 parts of water to 1 of 

 the salt, and whose freezing point was consequently 8f ° into the apparatus, he 

 found the solution continued to contract till it was cooled to 17°, but had sensibly 

 expanded by the time it was cooled to 15°. As no mention is made of the con- 

 tinuance of the experiment, we are led to conclude that it terminated at this 

 point. But from it he considered himself wan-anted, as far as one experiment 

 goes, to draw the conclusion, that the combination of a salt with water has no 

 other effect upon its quality of expanding by cold, than to depress the point at 

 which that quality begins to be sensible, just as much as it depresses the point of 

 congelation. 



Relying upon this experiment, subsequent ^\Titers considered the general law 

 established, and some of them made application of it to sea- water, and reasoned 

 upon the effects of it in accounting for some oceanic phenomena. 



It cannot be denied that a solitary experiment, if judiciously contrived and 

 carefully conducted, may afford sufficient proof of a particular fact ; but no single 

 experiment can warrant a general law, embracing circumstances different from 

 those of the individual trial. 



Two circumstances regarding the experiment now quoted cannot fail to ex- 

 cite much surprise. The first is, that Sir Charles stopped in the very threshold, 

 and did not continue it to its legitimate termination. It is astonishing that so 

 able and so patient an experimenter did not, to render the experiment conclusive, 

 or indeed worthy of any confidence, continue the application of cold till the in- 

 closed fluid was reduced in its temperature to its freezing point, with the view of 

 observing whether it continued to expand till it arrived at that temperature, as 

 is the case with pure water ; and farther prolong the experiment, by applying 



