64 Remarhs on the recent Conference at Vienna on 
as the hollows and bottoms, by the cold air flowing down into 
them, while the fields lying at higher levels escape injury. 
A study of the alleged efficacy of smoke in checking the 
radiation and prevention of frost would be most valuable, and 
also of the benefits said to be derived from sweeping a rope over 
a field at sunrise, so as to brush off the hoarfrost before the sun 
shines on the leaves. 
In connection with this action of frost a most remarkable 
experience of Mr. Buchan's deserves notice. It is given in the 
' Journal of the Scottish Meteorological Society,' vol. iv. p. 147. 
In a nursery-garden a net had been stretched over one bed, out 
of four, of ash-seedlings. The net had holes in it, and was 
thrown back at one corner. The night was clear, with a very 
light breeze, and in the morning it was found that the plants 
covered by the net were damaged, while those in the uncovered 
part of the bed, even those opposite the holes in the net, had 
escaped. The destruction was greatest on the sides of the bed 
and in the furrows. 
Mr. Buchan's explanation, which is evidently the true one, 
is that the net checked the motion of the air, and allowed 
radiation to exert its full effect. Over the uncovered plants 
the wind, though very light, removed the cold layer of air as 
fast as it was formed, so that the temperature never fell low 
enough to produce hoarfrost. In this case, therefore, the very 
device adopted to prevent injury from frost had aggravated 
the damage by interfering with the freedom of motion of the 
lower stratum of the air. 
Thermometers for measuring the minimum temperature on 
the grass should be placed on props at about 2 inches from the 
soil, at the level of the tops of newly mown grass. 
R. 10. " It seems most important that the relation between the radiation 
imder a cloudless sky and the humidity of the atmosphere should be carefully 
studied at large observatories." 
K. 11. "The methods of photometric observation, with especial reference 
to the chemical action of light, should be perfected by experiments at scientific 
institutions, in order to obtain a good chemico-photometric instrument." 
The objects mentioned in these two resolutions stand in need 
of more careful investigation. As regards the action of light, 
no instrument as yet invented is either quite satisfactory in its 
results or easy of manipulation. 
R. 12. " U'he humidity of the atmosphere should be measured by the dry- 
and wet-bulb hygrometer and the hair-hygrometer, and, if possible, three 
times daily (one observation being taken in the early afternoon). 
" As to the apparatus to be used, the Conference recommends comparative 
observations with the complicated volume hygrometer of Schwackhofcr and 
the simpler ajjparatus of Edlmann of Munich, in order to determine which 
of these arrangements should be finally recommended for use in observatories. 
