130 GREATEST DENSITY OF WATER. 



In the first interval, which comnnences with the change 

 of the current from clown to up, we observe the top loses 

 4'', and the bottom none. The bottom losing nothing is un- 

 accountable, when the ascending force was a minimum, ex- 

 cept on the supposition that the cooling liquid at bottom 

 during this interval was 38 or 40** instead of 32°. The third 

 interval gives 2° descent at bottom, and less than 1° at top; 

 this cannot be the effbct of an ascending current ; and still 

 less can the changes in the fourth and filth intervals be as- 

 cribed to the same cause. 



By frequent trials with a jar of 8 inches deep, and 2f dia- 

 meter, containing water of 40", and plunged into an ice-cold 

 mixture, to the same level, in a jar of 7 inches diameter, I 

 have found the thermometer at bottom always descends to 

 38" before the top one ; this last generally passes the other 

 about 37°, and even after remains lowest : after being 10 mi- 

 nutes at rest the top thermometer is about 35°, the bottom 

 about 37°, and the water at the bottom of the jar at 35°, the 

 air being; 40^. 



Examination 

 of Dr. Hope's 

 third experi- 

 ments. 



Dr. Hope's tl)ird experiment is an instructive one, and the 

 conclusion he derives from it is admitted ; namely, that water 

 of 32° is not specifically heavier than water of 40°. But 

 whether arc wc to infer from it that water of 40° is cq7/al to 

 water of 32° in density, or that it is svpciior? I think the 

 former. Whenever a column of water of 32° is situated on 

 another warmer column of the same density, (whether it be 

 40 or 48°) there can be no current generated from the mu-> 

 tual interchange of heat of the two columns, neither imme- 

 diately nor remotely. The connecting film, or stratum, will 

 indeed instantly assume the intermediate temperature of 

 greatest density (of 35 or 40°), and the contiguous strata 

 above and below will gradually shade oiY into warmer and 

 colder water ; hence the horizontal stnita will be of different 

 J specific gravities, but the perpendicular columns of particles 

 Avill all be of the same gravity, and therefore no motion ensue. 

 J^'ow docs not the experiment testify that this state takes phicc 

 when tlie tcmperfiture is at 40", and not at 48°? Hence we 

 jnust infer from it that water of 40° is of the same specific 

 1 aruvitv 



