5 lH SCIENTIFIC RECORD FOR 1883. 



-which the whole apparatus would sink beneath the river, then it is sup- 

 ported by two wires. (Z. 0. Q. M., xvn, p. 3G7.) 



Th. Langer publishes comparative observations with four Piche evap- 

 orimeters exposed under various conditions : (1) in free sunshine and 

 wind; (2) freely near a large mass of water; (3) shaded by tree or 

 house ; (4) within a shelter. The relative quantities evaporated were : 

 100, 98.3, 98.5, and 62.0, respectively. Langer concludes that for the 

 sake of uniformity it will be advisab e to use only evaporimeters lo- 

 cated within shelters, as thereby the variations due to temperature of 

 the water in the tube are greatly diminished. [As the direct effect of 

 sunlight or solar heat upon the water in Piche's tube can easily be obvi- 

 ated by adapting a small shade, there seems no reason why the whole 

 apparatus thus shaded should not be hung in a free exposure to the 

 wind, whereby the above relative percentage of 62 would undoubtedly 

 be increased.] (Z. 0. 0. 3L, xvn, p. 375.) 



Of all the recent contributions to hygrometry, the short memoir of 

 April 8, 1883, by Pernter, "Psychrometer Studien" (Sitzungsberickt of 

 the Vienna Academy, vol. lxxxvii, 2 Abtheilung), is so excellent a sum- 

 mary of the present state of our knowedge of this subject that the fol- 

 lowing historical and critical portions are worthy of being reproduced 

 in this place : 



"In recent times the psychrometer has been again much studied, 

 since we have endeavored, both theoretically and experimentally, to 

 arrive at a more accurate formula for the computation of the atmos- 

 pheric moisture from the psychrometric data.* By the assistance of the 

 Eoyal Academy of Sciences of Vienna it was also made possible for me 

 to institute comparisons of psychrometers on the Ober at an altitude of 

 2048 meters above the sea-level. The apparatus that I applied to this 

 purpose were: (1) a Wild's ventilation psychrometer; (2) a Regnault's 

 dew-point hygrometer; and (3) a Schwackkofer's volume hygrometer." 



[As these observations extended only over a few weeks, and were con- 

 fessedly unsatisfactory, I need give only the following abstract of this 

 portion of Pernter's memoir : 



" Let t — dry -bulb temperature in Celsius degrees. 

 V = wet-bulb temperature. 

 t — observed dew point temperature. 

 p = true atmospheric vapor tension corresponding to to. 

 Pi = the vapor tension corresponding to t'. 

 P = atmospheric pressure in m m." 



* Blanford, Journal Asiatic Society of Bengal, vol. xxv, part vi, 1876. 

 Chistoni, Memorie e Notizie Meteorologiana Italiana, anno 1878, fasc. 1, 2, and 5. 

 Chistoni, Annali della Meteorologi, Part I, 1880. 

 Sworikin, Repertoriuni fur Meteorologi, vii, No. 8, 1881. 

 Angot, Jonrnal de Physique, 2d series, 1882, No. 1, p. 119 



Maxwell and Stefan, Zeitschrift d. osterreichischen Gesell. Meteorologie, bd. xvi. 

 (Maxwell's original study is published in the Article Diffusion, Encyclopedia Bri- 

 tannica, 9th ed., vol. VU.) 



