METEOROLOGY. 289 



mining the temperature of lakes, springs, and rivers at slight depths as 

 adopted at the Bavarian stations. [As similar observations are made 

 at all the Signal Service stations, and are desirable for all ])arts of the 

 world, it is well to establish uniform rules and methods.] In Bavaria, 

 as in the United States, a small metallic vessel is lowered to the desired 

 depth, tilled with water, and brought to the surface. The thermometer 

 being always in place within the vessel, the reading should be made as 

 soon as possible after pulling the apparatus up. Among the precau- 

 tions to be observed, the most important is the necessity for allowing 

 the whole apparatus to remain in the water at the proper depth for a 

 sufficiently long time before the observation is to be made. Since the 

 water penetrates into all parts of the apparatus as it is lowered into 

 position, we shall obtain ouly an average indefinite temperature datum 

 unless the whole is left at the proper depth until the water and the metal 

 attain the proper temperature ; in fact, it is best to leave the apparatus 

 in the water for the whole.time intervening between two observations. 

 With the apparatus used in Bavaria Dr. Lang finds that two or three 

 minutes, at least, are required before the thermometer withiu the case 

 experiences any change of temperature, after being taken out of the 

 water. (Z. 0. G. J/., xviii, p. 307.) 



121. A. Angot, of Paris, publishes in the annals of the Central Meteor- 

 ological Bureau a new determination of the constant of the j^sychrome- 

 ter formula, based on 3,070 comparisons with dew-point api^aratus, and 

 made partly at Paris, and partly on the summit of the Puy-de-Dome. 

 He finds that the value of A varies with the difference t — t', and con- 

 structs tables accordingly. 



122. [The results of Angot's work seem still to require revision in 

 order to adapt the formula to the extreme conditions which are found 

 in the United States. It has, therefore, been found necessary to pur- 

 sue an extensive further system of observations at Washington, Pike's 

 Peak, and Yuma, the results of which will be eventually deduced by 

 Professor Ferrcl, of the Signal Office, who has already completed a 

 thorough analytical study of the theory of the psychrometer. It is, 

 however, evident that the various forms of dew-point apparatus have 

 also peculiar systematic errors, and our next attention must be given to 

 these.] 



123. xV. Sprung suggests a new method for determining the dew- 

 point. He says, correctly, that it is difficult to determine the exact 

 moment when condensation begins in the ordinar}^ use of the Regnault 

 ai)paratus, and esi)ecially when the temperature is below freezing, lie 

 suggests that it would be much more convenient and safe to observe 

 the moment of condensation when the cooling of the air takes ])laee, 

 not in a thin layer, but through its whole mass, so that the con<lensed 

 vapor shall appear as fog. He p'roi)oses to produce this condensation 

 by a rapid chauge of volume, using a small air-pump, connecting with 

 it a cylindrical receiver whose ends are closed with brass plates 3 the 



S. :Mis.^)3 19 



