NATURAL PHILOSOPHY. 137 



gical surface which would be presented if the earth were stripped of 

 its fluid coating. At present the number of unknown quantities in 

 an inquiry as to the earth's internal structure was greater than the 

 number of conditions ; but by knowing the true surface, and adopting 

 the results of established physical and hydrostatical laws relative to 

 the supposed internal fluid mass, we should be able to establish as 

 many equations as we have unknown quantities, and thus obtain a 

 solution. Professor Stevelly stated, that the exact spheroidal form 

 of the earth and the direction of gravity at each part of its surface 

 were not so completely determined as the remarks of Professor 

 Hennessy would lead a person to suppose. Very interesting papers 

 printed in the last volume of the Transactions of the "Roj'al Society, 

 by Colonel Sir Henry James and Captain Clarke, had shown con- 

 clusively that not only did the spheroidal form of the earth, as deduced 

 from the great Ordnance Survey of the British Islands, differ some- 

 what, from that considered as most suitable to the form of the earth 

 as derived from a comparison of all observations ; but even particular 

 localities had the plumb-line so affected by local circumstances, that 

 the form, as deduced from particular portions of the Survey, differed 

 sensibly from one another. Thus, the plumb-line near Edinburgh 

 was found to be affected not only by the proximity of Arthur's Seat 

 and the Calton Hill, but even in the defect of matter in the Frith of 

 Forth, and.the excess in the distant Pentland Hills, were shown to 

 exercise important influences. Colonel Sir H. James showed by 

 various examples that the method of grouping the measurements of 

 different countries proposed by Mr. Hennessy would not, in the 

 present state of these measurements, lead to the exact results he 

 supposed. He then pointed out circumstances not only respecting 

 the Russian measurements, but even the French, which would make 

 a re-examination of them not only desirable, but necessary. 



ICE PHENOMENA. 



Mb. B. F. Harrison has read to the American Association a paper 

 on the Solution of Ice in Inland Waters, accounting for the sudden 

 disappearance of ice by a theory based upon observations upon a 

 small lake in Connecticut, so hedged in that only the south and 

 southwest winds blow upon it. No large stream feeds it, and its 

 outlet is small. January 23, 1860, the ice was ten or eleven inches 

 thick ; the temperature of the ice varied from 34° just below the ice 

 to 43.1° at the bottom ; average 3Sg°. March 6, the ice disappeared 

 very rapidly, about one-third disappearing during two hours. The 

 mean temperature of the water was then 414°. He concludes, 

 therefore, that the solution of the ice is caused by heating the water 

 upward from the bottom, since the temperature of the air was less 

 than that of the water. 



Prof. Elias Loomis has read to the above Association a paper on 

 Natural Ice-Houses and Frozen Wells. These occur in places where 

 the ice accumulates in the cold season, and remains during the sum- 

 mer months, or even the entire year, although the mean temperature 

 of the neighbourhood may be io° or 15° above the freezing point 



