202 Experiments on Sea- Water. 



on needles, the bars being out of the sphere of the cold ; and, 

 moreover, its effect on bars, the needles being in their turn out 

 of the sphere of the cokl ; and lastly, the effect of the same on 

 both of them at once. A more favourable stratification of the 

 mixture allowed me to observe more decided effects at each 

 combination, notwithstanding the general temperature of tho 

 room being lower than yesterday (both of them from 60''-70°), 

 and notwithstanding I had no larger apparatus for cold than 

 the former ones. They were, however, adequate to the gra- 

 duated series of the bars, lying sometimes on their sides be- 

 tween the two parallelopipeds joined together, and sometimes 

 separated only by their joined depths or lengths from the 

 neeilles. I have even plunged needles and litde bars into ice, 

 and used both of them after drying them. The results have 

 been ahvays the same: the lower the temperature and the 

 longer the immersion of the bars and needles, each separately 

 or both at once, in the frigoriiic sphere, the greater the pa- 

 ralysis. Wliat influence, therefore, must not be exercised on 

 the currents of needles, as well as sometimes on the terrestrial 

 ones, by the low temperature of the polar regions? — I am in- 

 debted for the idea of these experiments to the simple obser- 

 vation of Captain Ellis, who, meetmg ice mountains in Hud- 

 son's Bay, saw his needles sluggish at their approach, and says 

 that he restored them to their Ibrnier activity by warmth. Far 

 from reasoning on the circumstances, he has the air of repeat- 

 ing the fact as a kind of mysterious accident. What a dif- 

 ference between that transient rough observation and the re- 

 sults we have obtained ! Such is the progress of science, 

 aided by time, zeal for experiment, and skill in observing ! 



This morning, too, I have completefl, with Mr. Garden, 

 the experiments happily begun yesterday at Mr. Gary's about 

 freezing sea-water with the same frigorific mixture used in 

 the magnetic experiments. Sea-water from near South End 

 (Essex), sold at the Establishment of the Sea-water Baths in 

 George-street, Adelphi, freezes when in perfect quiet at only 

 about 18" F., or at the utmost from IS** to 20", when in small 

 quantity and agitated on purpose. At 22" it was impossible 

 to obtain ice through any length of time. What credit then 

 shall we give to what Thomson says, even in the sixth edition 

 of his " System of Chemistry," on " Nairne's authority from 

 the Philosophical Transactions," that sea-water freezes at 28"*5 

 Fahrenheit ? By die by, the general temperature of the room 

 was rather high, to favour as much as possible the frigorific 

 effects of the mixtures ! The ice obtained from the water of the 

 sea may be nearly deprived of salt, particularly when obtained 



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