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LXIT. Intelligence and Miscellaneos Articles. 



LUNAR RADIATION. 



To the Editors of the Philosophical Magazine and Journal* 

 Gentlemen, Oxford and Cambridge Club, Nov. 19, 1861. 



In your November Number there is an account by Professor 

 Tyndall of some observations with a thermo-electric pile, in the 

 course of which it appeared that it " lost more heat when presented 

 to the moon than when turned to any other portion of the heavens 

 of the same altitude ; " and there is a theoretical explanation of this 

 fact as an indirect effect of the moon's heat, dispersing the " small 

 quantity of precipitated vapour" which it appears was then floating 

 in the atmosphere, and so facilitating radiation from the instrument. 



Unless my memory is deceived, Sir John Herschel, in one of the 

 earlier editions of his 'Astronomy,' described light clouds as, in like 

 manner, dispersing as they came between his telescope and the moon ; 

 but in the edition of 1858, here at hand, I see the phrase is " the ten- 

 dency to disappearance of clouds under the full moon," which may mean 

 a very different thing, viz. a tendency to clear skies when the moon is full. 



That the heat of the full moon may tend to clear the upper atmo- 

 sphere, and so be the cause of cold below, may be true ; but it does 

 not appear to me that this can be the explanation of Professor Tyn- 

 dall's fact, or of Sir J. Herschel's, if I state it correctly. 



High in the air, in the region in which the moon is seen, there is 

 cloud or vapour observed. The moon may have diminished, but it 

 has not destroyed it generally. How then is that particular portion 

 which happens to intervene between the observer's instrument and 

 the moon more under her influence than any other equal portion ? 

 If a hundred observers were gazing at her at the same time within 

 a few miles of each other, a hundred different portions of the haze 

 would so intervene ; and to suppose each of these dispersed, is to 

 suppose the haze not to exist. 



It is possible that a full examination of all the circumstances of 

 Professor TyndalTs six experiments — the area embraced by his 

 reflector, the probable height of the vapour in the air, the extent of 

 the sweep he took with the instrument, &c. — might remove some of 

 the difficulty I feel in admitting the explanation he proposes ; and in 

 the interest of exact science I venture to call his attention to the 

 matter. ______ D. D. Heath. 



ON THE DIHEXAHEDRAL CRYSTALS OF SULPHATE OF POTASH. 

 BY KARL RITTER VON HAUER*. 



The supposed dimorphism of the sulphate of potash, as K. Von 

 Hauer has proved, rests only on external appearance, as in reality 

 this salt in a state of chemical purity constantly affects forms of the 

 prismatic system, and when appearing in forms of the rhombohedral 

 system invariably contains a certain quantity of anhydrous sulphate 

 of soda. This bibasic salt is known to be produced at Glasgow, in 

 the shape of hexagonal plate-like crystals, by the evaporation of a 

 solution of kelp-ash. A mixture of both these sulphates (potash and 

 soda), inspissated and left to crystallize, invariably gives no longer 

 hexagonal plates, but exclusively dihexahedrons (double hexagonal 

 * Translated by Count Marschall, 



