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Miscellaneous InteUlgence. 1 57 



Anotlier period of tea days commenced Jan. 3d, 1835, during wtich 

 tlie average of the morning observations was - Ib^-Q^ and of the evening 

 -5°-3. Lowest -32^ 



Anotlier period of eight days commenced Feb. IStb, 1849 ; average of 

 morning observations -15°'4, and evening '-1°*4. Lowest -21°. 



Another commenced Jan. 16, 1852, and continued seven days; the 

 morning average was - ll^'S, evening -4^*4. Lowest - 23°. 



The recent period of four days, from the noon of Jan. 22, 1857, gives 

 a morning average of -25°'8*, evening -12°''i'; noon -l°-0, and low- 

 est -3 9^ 



The mercury did not quite congeal in our thermometers on the morn- 

 ing of the 24tb of January, but w^ould doubtless have done so at the 

 Hanover bridge, in the valley, 140 feet lower than our village, liad not 

 the owner of the instrument, on perceiving the rapid descent of the mer- 

 cury on the evening of the 23d, taken it in, to prevent its freezing and 

 bursting. He was not aware that mercury, unlike water, contracts, on 

 congealing, instead of expanding. In low grounds surrounded by precip- 

 itous hills the temperature, when the air is still, is generally some degrees 

 lower than in more elevated localities. Thus at the White River Junc- 

 tion (which is about 187 feet lower than our village), and at several other 

 places iu our vicinity, the mercury is reported to have frozen. It may be 

 proper to remark, that the carefully conducted experiments of Dr. Kane, 

 in his Arctic expedition, show that the specimens of distilled mercury 

 which he subjected to trial, congealed at temperatures from -38°-5to 

 — 41^*5, and after congealing, contracted so as to give an indication of 

 -44, The observations of Sir Edward Belcher confirmed these results, 

 the congealed mercury, in his experiments, contracting to - 46°. Pouillet 

 gives the point of fusion of mercury at -39°'2. The results of spirit 

 thermometers, at a very low temperature, should be received with cau- 

 tion. Dr. Kane found that six spirit thermometers which were selected 

 as the most consistent of nearly thirty, and all of which at temperatures 

 above -40 atrreed within 1°'8, read as follows at noon, Feb. 5, 1854: 



-71°, -63°, -54°, -50°, -50°, thus differing 21 degrees. This proba- 

 bly o\ving to the diflfcrent conditions of the alcohol with which they were 

 filled, in respect to purity, and the quantity and quality of coloring mat- 

 ter employed. y, 



Dartmouth College, Jan. 31, 185Y. 



2, Filtration through Sand. — Experiments by ^fr. Henry M. Witt, at 

 the Chelsea waterworks, (England) have proved that by simple filtration 

 of water through sand, soluble salts as well as suspended matters are sep- 

 arated. Out of 65'52'7 of solid residue dissolved and suspended, 24-237 

 were separated, including Y'559 of soluble salts, (1-820 of these chlorid 

 of sodium). From water containing 55*60 of solid residue, 32'75 were 

 thus separated 3'404 of which were dissolved salts. Hence mere perco- 

 lation through sandy strata for long periods may separate dissolved saline 

 ingredients from waters. Mr. Witt applies the facts to explain the occur- 

 rence of freshwater springs on coral islands, that ebb with the tide. 

 PhiL Mag. [4] xii, 23. But here Mr. Darwin's explanation seems most 

 reasonable: — that the freshwaters are from the rains; and that beino- 

 detained upon the coral rock, and at the same time being lighter than the 



