204 



The result was, that the fluids descended in the tube from cold, 

 and ascended from heat uninterruptedly, as mercury and alcohol 

 do ; and did not, like water, present any appearance of interruption 

 in their course or retrocession. 



2d, But as doubt must always hang over experiments conducted 

 in this manner, in consequence of the interference of the changes in 

 the capacity of the thermometric instruments, arising from the alte- 

 rations of temperature, he resorted to the method described in his 

 memoir read to this Society in 1804. This consists in discovering 

 the eflFects of heat and cold on the density of fluids, by ascertaining 

 by thermometers placed near the top and bottom of a column of the 

 fluid, the direction of the currents induced in the fluids, fully 

 assured, that the rarer will invariably ascend, and denser descend. 

 Proceeding in this manner, Dr H. found that, when a frigorific mix» 

 ture was applied to the middle of a column of sea water at the 40th 

 degree, the cooled water immediately began to descend to the bot- 

 tom, and continued to do so steadily, till the thermometer at the 

 bottom indicated the congealing temperature of the fluid ; and 

 asain, that when heat was thrown into the middle of a column of 

 sea water cooled to its freezing point, the heated fluid immediately 

 began to ascend, and continued to do so uniformly and uninter- 

 ruptedly. 



From this and the preceding series of experiments, Dr Hope 

 considered himself warranted to conclude, that the strange anomaly 

 Avhich fresh water presents does not exist in sea water. — That at 

 all temperatures above its point of congelation, it is expanded by 

 heat and contracted by cold, and that its maximum of density does 

 not occur at 7^° above its point of congelation, as is the case with 

 pure water. 



Dr Hope did not touch the very difl&cult and perhaps indeter- 

 minable question, viz. the temperature at which sea water and so- 

 lutions of salt have their maximum of density ; reserving that 

 question, and ihe consideration of the effects of various substances 

 soluble in water in rendering this fluid obedient to the general law 

 of expansion by heat and contraction by cold, for another memoir. 



