97 



VIOLLE'S CONJUGATE BULBS. 



The refined methods for iiieasnrino; sohir radiation adopted by 

 Violle (1879) in his absohite actinonietry can hardly be utilized in 

 agricultural investigations oAving to the labor of using the apparatus. 

 But the continuous register ol)tained 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 Marie-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 Marie-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 (189l'). 



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. xV 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 licjuid can be measured. 



Under the action of the radiation from the sun and the slcy the 

 l>lue 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 c(mdensation in D is a 

 source of heat, while the vaporization in A is a source of cold. The 

 heat given off by condensation must e<iual that consumed in evapoi-a- 

 tion, and is drawn off from the apparatus by the action of the cool 

 20G7— 0.5 M 7 



