PRACTICAL RELATIONS OF SCIENCE. 
115 
composition of air and water, soils and minerals, vegetables 
and animal productions, and the changes that accompany life 
and death, nutrition and decay, to an extent that has thrown 
as much light on the progress of Agriculture, as it has shed on 
Arts and Manufactures. 
We now know the true component parts of numerous vege¬ 
tables, and if they are not to be found in the soil, in the 
atmosphere, or in the water, vain must every attempt be to- 
stimulate their production, without adding at the same time the 
absent ingredients in a suitable form. We may suppose a field 
whose mineral constituents are such that the action of air and 
water, heat and cold, return annually as much of the elements 
to it as the crops may remove. But this is an exception to 
the rule. The tendency in all ordinary cases, is for the farmer 
to exhaust his soil, except where a river, like the Nile in its 
annua? inundations, restores by mechanical deposition, and 
precipitation from solution, the required ingredients. Hence 
the analysis of plants and soils is the only true basis for Sci¬ 
entific Agriculture. 
But while many admit the importance of these conclusions, 
they are disposed to assert that such knowledge is often too 
refined and too difficult of attainment to come within the reach 
of the farmer. The reply to this is evident. Professional 
men must be employed for the more complex and difficult cases, 
but many are the instances where even a very moderate amount 
of chemical knowledge has proved invaluable. Let me quote 
one or two instances that have come under my own observation. 
A farmer in the vicinity of Edinburgh had long been puzzled 
by the very bad crops from a field to which he had paid the 
most scrupulous attention, according to the ordinary rules of 
farming. Chemical aid having been called in, it was ascer¬ 
tained that the field in question was subject to injury from the- 
variable overflow of an acid chalybeate spring. By the addi¬ 
tion of lime to the water, so as to neutralize the acid, further- 
injury was prevented, and abundant crops obtained in future. 
[Here Dr. Reid illustrated, experimentally, the tests used on- 
this occasion, and the facility with which they were applied.]' 
