97 
VIOLLE’S CONJUGATE BULBS. 
The refined methods for measuring solar radiation adopted by 
Violle (1879) in his absolute actinometry can hardly be utilized in 
agricultural investigations owing to the labor of using the apparatus. 
But the continuous register obtained by him by means of thermo- 
electric apparatus is an important improvement in the methods avail- 
able for comparing climates. On the other hand, Violle has sug- 
gested a modification of the conjugate thermometers which he calls 
his “ conjugate bulbs,” which is worthy of consideration, although far 
from being as sensitive as Marié-Davy’s apparatus. These bulbs are 
made of thin copper, one of them blackened and the other gilded 
on the outside; the interiors are blackened, and the thermometer 
bulbs within them are also blackened. This apparatus has an appar- 
ent advantage over Marié-Davy’s, in that the sunlight is not required 
to pass through glass before striking the thermometer. It would 
appear likely that with smaller bulbs (Violle uses 1 decimeter in 
diameter) and with more sensitive thermometers Violle’s method 
might give better results and be worthy of recommendation to agri- 
cultural investigators. The results given by his apparatus have need 
to be reduced by some method based on the considerations indicated 
by Ferrel (1891). 
BELLANI’S RADIOMETER OR VAPORIZATION ACTINOMETER. 
Among the many devices invented for the purpose of obtaining, 
at least approximately, the sum total of the effect of sunshine received 
during any day by a given plant is one that has been used for a few 
years at the Montsouris Observatory, and is a modification of an 
apparatus originally devised by the Italian physicist, Angelo Bellani, 
which is thus described by Descroix (p. 128, Annuaire de Montsouris, 
1887; see also the Annuaire for 1888, p. 206, where it is called the 
lucimeter, although it does not measure light properly so called). 
The vaporization actinometer or the Bellani radiometer as modi- 
fied at Montsouris consists of a bulb of blue glass A of about 60 
mm. in diameter, inclosed within a larger bulb B of colorless glass. 
The space between the two bulbs is a vacuum. <A is two-thirds filled 
with a volatile liquid and the space above it contains only its vapor, 
which passes through a curved tube down into a large bulb C, of clear 
glass, and thence down into the vertical tube D, which is graduated, 
and where the condensing liquid can be measured. 
Under the action of the radiation from the sun and the sky the 
blue bulb A is warmed more than the bulb B; a distillation takes 
place from A and the condensed liquid is collected in the graduated 
tube D, where its volume is measured. This condensation in D is a 
source of heat, while the vaporization in A is a source of cold. The 
heat given off by condensation must equal that consumed in evapora- 
tion, and is drawn off from the apparatus by the action of the cool 
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