26 
ROYAL HORTICULTURAL SOCIETY. 
would suffice for such observations ; but other instruments for greater 
depths, on the same principle, could be made as required, under the 
same conditions of examination. 
It is exceedingly desirable to be able to ascertain the degree of 
temperature surrounding roots nourished with different manures, 
particularly those which readily accept nourishment, and to ascer- 
tain whether the same manures in the same proportions yield the 
same temperatures with different species, or whether the tempera- 
ture, however derived, which is best to bring one species of plants 
to perfection is the best for other varieties of that species. 
This instrument has been submitted to the Scientific Committee 
of the Royal Horticultural Society, under whose auspices, in con- 
nection with myself, it will be made. 
yi. On a Dry and Wet Eiilb Thermometer. By James Glaishk.R, 
r.E.s. 
[Read June 26, 1872.] 
An exact knowledge of the state of the humidity of the air is as 
important as that of its temperature, in all closed buildings used 
for horticultural purposes. When plants are imported from other 
climates, their more or less capability of acquiring maturity is 
much dependent on the more or less approximation to the climate 
from which they came, both in its degree of humidity as well as 
its temperature. Ey the use of the dry and wet bulb thermometer, 
both these elements are known, and the one now exhibited (fig. b) 
is fixed on a metal frame, so that it cannot be injured by water in 
the greenhouse. I consider that instruments of this class, for this 
purpose, should be good and inexpensive. The pair of thermometers, 
as shown, are very nearly without errors at every part of their 
scales, and could be used for outdoor determinations of temperatui^e 
and humidity of the air if necessary. Mr. Ackland (Horne and 
Thornewaite, 123, Newgate Street) has agreed to furnish these 
instruments thus mounted at 15s. the pair, upon the agreement that 
he will send them to me for examination before mounting, and sell 
those only to horticulturists which are furnished with my certifi- 
cate of their accuracy, and that I am permitted to reject all instru- 
ments which may have an error as large as three -tenths of a 
