36 
COMPARATIVE COLDNESS OF LOW AND ELEVATED LOCALITIES. 
and failures which attend a vague and random use of terms, and shall no longer 
take it for granted that the loam of a Middlesex nursery is identical with one so 
called in Yorkshire. 
But there is also vegetable nutritive matter in all loams, and a portion of this is 
soluble in water : the actual weight of it may be ascertained with comparative 
accuracy by taking a fourth parcel of the dried, powdered loam, and keeping it at 
a full red heat till there remain no black colour in the earth after becoming cold ; 
the loss of weight will then determine the quantity of vegetable fibre, or of the 
substance now called hiimus^ which the loam contained ; and thus its fertilizing 
qualities will be more readily estimated. It is astonishing to what extent sand may 
exist in a loam, and yet leave it hard bound after watering ; a sharp, harsh, gravelly 
grit may form three parts of four of a loam that then remains quite intractable ; 
therefore, we advise the gardener to attend strictly to the texture of the sand, 
which, in the best loams we have ever seen, is finer than silver sand :— upon 
this ingredient depends the softness of the loam, and its fitness for the purposes of 
pot culture. If equal parts of this fine earth and heath-soil be required for a 
certain tribe of plants, a gardener who has a stiff and rigid loam only at command, 
must employ but one third of it, and even less than that, otherwise he must fail in 
keeping his plants in health. 
Of leaf-mould and manure, we must speak in an another article. Sand — pure 
sand — requires no analysis ; but pit-sand should be washed. Heath soils differ 
exceedingly, yet all contain iron. They only require the operation of fire to ascer- 
tain their relative value. Each specimen should be dried, weighed, and burned 
in a Hessian crucible, or small iron ladle, till nothing but sand remain ; and then the 
loss of weight will show the quantity of vegetable matter that each contained. 
COMPAHATIVE COLDNESS OF LOW AND ELEVATED 
LOCALITIES. 
It appears perfectly plausible to suppose that hilly situations, exposed to all the 
violence of the bleakest winds, should be considerably colder than sheltered valleys, 
or level districts ; and, as far as the human feelings are concerned, the assumption 
is mainly correct. But those who have observed the phenomena of nature, and not 
allowed any fact to pass unnoticed, or without seeking some satisfactory explication, 
well know that vegetation is affected very differently to man under certain conditions 
of temperature, and that frost, which is generally most fatal to plants, is far more 
prevalent in valleys than on hills. 
This statement is by no means novel. It has long since been ascertained that 
the coldest air has the greatest specific gravity, and must necessarily, by its own 
force, accumulate in the lowest localities. Moisture, too, being more abundant in 
