203 



that it arises anterior to the pons or nodus cerebri, in order to be 

 free of the intricate texture of nerves which have reference to the 

 complex operations of the trunk and limbs ; that the necessary 

 combination of motion and sensation in the eye, uncontrolled by 

 remote relations, and free of the combined operations of the frame, 

 is the reason both of its peculiar origin and of the intimate combi- 

 nation of a sensitive and motor root. 



3. Inquiry whether Sea Water has its Maximum Density at 

 some degrees above its freezing point, after the manner 

 of fresh water. By Dr Hope. 



Dr Hope stated that it has been considered a matter of consider- 

 able importance in the reasonings of geologists and hydrographers 

 respecting some oceanic phenomena, whether sea water obeys at all 

 temperatures the general law of expansion by heat, and contraction 

 by cold, or, after the manner of fresh water, observes the anomalous 

 course of contracting by heat, and expanding by cold, during a short 

 range of temperature near its congealing point. 



In 1788, Sir Chai-les Blagden concluded, from a solitary experi- 

 ment, that a solution of common salt, chloride of sodium, in water, 

 began to expand, when cooled to about 8° above its freezing point ; 

 and thence it has been inferred, that all solutions of salt will exhibit 

 the same phenomenon ; and the law has been laid down, 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 con- 

 gelation, and that saline solutions begin to expand at 7^° above 

 their point of congelation. Transferring these views to sea water, 

 its maximum density was supposed to be about 36^ ^ Various rea- 

 sonings were foujjded upon that supposition. 



Dr Hope then adverted to the discordant experiments of Dr 

 Marcet in 1819, of M. Erman in 1828, and of M. Despretz in 1836 

 and 1837. 



The object of Dr H.'s inquiries was to ascertain whether sea 

 water and stronger solutions of common salt are subject to the com- 

 mon law, or the anomalous aqueous one. He carried on the inves- 

 tigation in two modes, 1st, By employing thermometric glasses, 

 containing the saline fluid, and observing the descent of the fluid in 

 the stem during cooling to the point of congelation, and its subse- 

 quent ascent when again exposed to heat. 



