110 Sir J. F. W. Herschel's Notice of a remarkable Deposition 



filled, an equilibrium of temperature cannot be established 

 after any lapse of time. 



11. Corolla?y. — Since (art. 5.) we have found g = 2h in 

 the case of nature, we shall have for the expression of s upon 

 s 1 , or of s' upon s, 



a h s sin p . / sin <p 



But if the surfaces have unequal temperatures a and b, and 

 supposing, for example, that a is greater than b, the result of 

 their mutual action will be proportional to 



, 7 w s sin p . s' sin a 

 (a-b)h ^ r ? 



conformably to experience. 



XX. Notice of a remarkable Deposition of Ice round the 

 decaying Stems of Vegetables during Frost. By Sir John 

 F. W. Herschel, K.H. F.R.S. Src.$c. 



[With Figures: Plate II.] 



To R. Phillips, Esq. $c. 8?c. 



Dear Sir, 

 ^OME years ago during the first days of a sharp frost, my 

 ^ attention was attracted by the unusual accumulation of ice 

 round the roots and stumps of some dry and decaying thistles 

 in the fields ; while at the same time comparatively little hoar- 

 frost was deposited on wheat-stubble and other vegetables in 

 the neighbourhood. On examination I found it to incrust 

 the stalks in a singular manner in voluminous friable masses, 

 which looked as if they had been squeezed, while soft, through 

 cracks in the stems. It was chiefly or entirely confined to 

 the immediate neighbourhood of the root, the upper parts of 

 the taller unbroken stalks being quite free from it. This pe- 

 culiarity of situation, and the comparative absence of hoar- 

 frost elsewhere, induced me at the time to attribute it either 

 to some different cause from hoar-frost, or to some singular 

 modification of that atmospheric deposition by local and tem- 

 porary circumstances. 



The above observation was recalled to my recollection by 

 a similar phenomenon noticed on the morning of the 11th 

 instant, after a night of sharp frost, of the kind vulgarly called 

 " a black frost;" there being little deposition of hoar-frost 

 from the air, which was during^the night extremely tranquil, 

 with a scarcely perceptible current from the north-east. The 



