256 METEOROLOGY AND ALLIED SUBJECTS. 



desirous of making the instrument fully respond to the demands of the 

 present state of barometry, he jiroposes a new form which will, he 

 thinks, be more entirely free from errors depending on time and cir- 

 cumstances. He proposes to substitute some form of hydrostatic flota- 

 tion for the balance beam, baving found that a remarkable constancy 

 attends the measurements of bodies floating in mercury, while the fric- 

 tion is reduced to an inappreciable quantity. 



The device for registration (namely, a pencil or point pressed against 

 a sheet of paper continuously, or at regular intervals, by clockwork) 

 offers still some difBculty, which, however, can, we suggest, probably 

 be removed by introducing the features of Thompson's electric i)en, as 

 used with the Atlantic cable. Schreiber suggests photography, and 

 also glass plates covered with lamp-black, as a means of recording the 

 observations. He gives a comi)lete mathematical exposition of the 

 theory of the corrections to this new form of instrument and shows that 

 all constants and all sources of error can be determined in the instru- 

 ment itself, thus making it an independent standard and not an interpo- 

 lation barometer. Where the influence of temperature is large, it can 

 easily be computed. {Z. 0. G. 3L, XVI, 1881, p. 407.). 



Kohlrausch has suggested some improvement in his method of mak- 

 ing absolute measures of the intensity of terrestrial magnetism by 

 the galvanic method; in its latest form he overcomes the difficulties 

 due to the large dimensions of the instrument, the necessity of knowing 

 the curvature of the surface of the coil of wire, the determination of its 

 moment of inertia, and the accurate determination of the time. The full 

 description of his methods will be found in the "jSTachrichten" of the 

 Scientific Association of Gottingen, June, 1881. His method commends 

 itself especially in that observations of magnetic variation and the du- 

 ration of the vibrations are unnecessary; it will probably be adopted 

 by several of the observers on the international stations for Polar re- 

 search. {Z. 0. O. 3f., XVI, p. 473, 1881.) 



Sworikin has made an excellent study as to the reliability of the psy- 

 chrometer constant (A) and the eflect of the velocity of the wind. He 

 has used the Alluard dew-i)oint apparatus and the Schwack hofer 

 volumetric hygrometer as his standards of comparison. Belli, Eeg- 

 nault, and Chistoni had all shown that a regular gentle current of air is 

 essential to accuracy. Sworiken concludes: (1.) That the best value of 

 the constants give the following formula : 



X = f— 0.000725 (t-f) B. 



(2.) That the same formula applies for /' below as -well as above freez- 

 ing, contrary to the theories of August and Eegnault. (3.) For wind 

 velocities of 1.5 to 2.0°^ per second (3 to 4 miles per hour) the best results 

 are obtained (4) that the computed tensions of vapor are accurate to 

 within 0.1"'°^. {Z. 0. G. M., XVI, 1881, 434.) 



Dr. M. Thiesen has x)ublished, among the metronomical contributions 



