422 Miscellaneous Intelligence. 



takes place, by no means necessarily preceded by any gradual 

 diminution : the degree of this is very various, but frequently 

 so considerable as to make the difference between what would 

 generally be called very mild weather, and a pretty sharp frost. 

 I think I have on some occasions experienced in little more 

 than twenty minutes, a change which could hardly be less than 

 20°. The hoar-frosts of spring and autumn generally come on 

 at that time, and sometimes so suddenly as to surprise the 

 earth-worms, (which come out only in very mild nights,) and 

 freeze them in great numbers. The cold will frequently con- 

 tinue, for an hour or two after the sun is up, to be greater than 

 it had been in the night. In the remarkably hot summer of 

 1818, all the dew that fell was at that time ; the grass being 

 at midnight as dry as at noon. 



I shall be happy if these few hints have the effect of turning 

 the attention of the lovers of meteorology to an interesting 

 subject which has not hitherto been sufficiently investigated. 



While ray pen is in my hand, I cannot forbear suggesting 

 to your chemical correspondents the inquiry, (which, if it has 

 ever been satisfactorily pursued, I have not been fortunate 

 enough to see the result of,) into the formation of nitre in 

 plants : it is well known that the juices of some plants contain 

 nitrate of potash ; (among others, I have detected it in the 

 polygonum bistorta, called in English " red-legs," which, as 

 far as I can learn, had not been previously known to contain 

 it,) but the most remarkable circumstance is its appearance in 

 the ashes of a plant in which, before burning, there are no traces 

 of it. The plant is the common yarrow or milfoil, (" Achillaea 

 millefolium,") a strong decoction of which I ascertained to be 

 perfectly destitute of nitre ; while a part of the same parcel of 

 the plant, on being slowly burnt, afforded ashes very strongly 

 impregnated with it. The chemical Professor of this Univer- 

 sity will attest the fact, in case any doubt should be entertained. 

 It is hardly necessary to remark how much light a course of 

 careful experiments on this point would throw upon the 

 mysterious subject of the formation of nitre. 



lam. &c. &c. OXON^ 



