Agricultural and Forest Meteorology. 
65 
" Ordinary stations should, for the present, employ only the dry- and wet- 
bulb liygrometer and the hair-hygrometer." 
As regards hjgrometry, or the determination of the amount 
of vapour in the air, the state of our knowledge is far from 
satisfactory ; but, pending the result of such experiments as are 
indicated in the resolution, and are actually in progress in 
various laboratories, agriculturists must only content themselves 
with the dry- and wet-bulb hygrometer. 
The old hair-hygrometer, though much in favour on the 
Continent for use in cold climates, is not so much needed in 
these islands, where the frost is not so intense or lasting as, for 
instance, in Central Europe, and the instrument is scarcely used 
here. Nevertheless the appliances for such an ordinary observa- 
tion as that of the moisture in the air stand in urgent need of 
improvement. 
E. 13. " The Conference is of ojiinion that observations on evaporation are 
important, but that no existing instrument can be proposed for general and 
exclusive use. In fact, it is recognised as an immediate requirement to 
devise satisfactory apparatus which will admit of the accurate measurement 
of evaporation, not only from open water-surfaces, but also from different 
soils in the fallow and cropped state. 
" Meanwhile, observations on evaporation should not be omitted, but they 
should be conducted with simple forms of apparatus, especially such as 
depend on the princijtle of weight, as well as with Piche's evaporimeter, as 
proposed to be modified by Prof. Cantoni." 
Evaporation is a subject which has not yet, in this country, 
attracted the attention it merits, for few points can be of greater 
importance to agriculturists than the removal of water from the 
soil, of which process evaporation is one of the channels. 
The reason of our neglect of the observation is its inherent 
difficulty. No one can say that the evaporation from a dish of 
water placed on a grassplot gives a correct idea of the amount 
which would be removed in the same time from an equal area 
in the centre of a lake, while such an experiment can have next 
to no relation to the evaporation from the soil. This again 
varies largely with the character of the crop, as has been 
abundantly proved by the experiments at Rothamsted. 
The form of apparatus recommended is of the nature of a 
balance, in one scale of which a pan either of water or of earth 
is placed, and its loss of weight in a given time ascertained. 
Piche's small apparatus consists of a graduated test-tube 
filled with water and inverted, the mouth being closed by a 
disc of blotting-paper the size of a shilling, this latter is, 
therefore, the evaporating surface. 
R. 14. "Condensation should be observed in all its forms." 
K. 15. "The Confeience thinks that observations on dew are important, 
but, in the absence of a thoroughly satisfactory apparatus, all that is required 
VOL. XVII. — S. S. F 
