290 SCIENTIFIC RECORD FOR 1884. 



pistou of the pump to have its motion limited by a motionless screw so 

 that the exact amount of its motion and consequently of the expansion 

 and cooling of the air can easily be determined. 



124. [Esijy's nepheloscope seems to have realized Spning's idea. 

 Many observations with it are given in Espy's works.] {Z. 0. G. M., 

 XVIII, p. 403.) 



125. Professor Crova, in the Meteorological Bulletin of the depart- 

 ment of Hernault, gives some exami^les of the use of his new form of 

 dew point apparatus known as the hygrometer with interior condensa- 

 tion. The advantage of this method consists in this, that the precipi- 

 tation is not influenced by the currents of air, which by their strength 

 and variability interfere with Regnault's apparatus. Even with the 

 greatest dryness of the air Crova's apparatus gives good results when 

 Regnault's refuses to work. In the illustrative observations given by 

 Crova we find, as was to be expected, that Regnault's apparatus gives 

 dew-points too low by as much as 1^.6 C. [Z. 0. G. M., xix, p. 45.) 



126. R. H. Scott has published the results of observations made in 

 different forms of thermometer shelters and at different altitudes for the 

 purpose of determining the influence of these circumstances upon the 

 recorded temperature and moisture of the air. 



127. [As a means of deciding on the relative merits of various methods 

 of exposure of thermometers this important series of observations lacks 

 one essential, namely, simultaneous observations of the true tempera- 

 ture of the air of each locality taken by some method whose theory can 

 be accurately investigated ; this essential has lately been supplied by 

 Ferrel's studies into the theory of the ordinary thermometer, the whirl- 

 ing psychrometer, and other apparatus.] 



128. Taking these records as they stand, Hann shows that the daily 

 range of temperature diminishes with the height above ground by an 

 amount equal to lo.3 C.,in the annual means for exposures, respectively, 

 10 and 129 feet above the earth. The lower exposures invariably show 

 a higher vapor tension and dew-point than the upper, but the relative 

 humidity has no such regularity. Classifying the observations accord- 

 ing to the conditions of ihe sky, as being either perfectly clear or per- 

 fectly cloudy, rainj' or foggy, he finds that at all times of day, winter 

 and summer, during fog the temperature increases with the altitude. 

 The differences between temperatures at high and low stations are small- 

 est during rain. During clear weather, in the evening, the temperature 

 increases with the altitude, but at mid-day it diminishes rapidly; at 9 

 A. M., in clear weather, in winter, it is warmer above than below. {Z. 

 0. G. j¥.,xviii, p. 395.) 



129. Dr. R. Assmann in some remarks upon the sling-i)sychrometer, 

 states that an observation of the temperature of air perfectly free from 

 objectionable features is a matter of the greatest rarity in meteorology ; 

 so difficult is it to attain a thoroughly satisfactory exposure. Until re- 

 cently (and even now in many Prussian, English, American, and otUei' 



