B. TiMiKESTEIAL PHYSICS AND METEOROLOGY. 105 



moirs of the Academy of Sciences of that city, it consists es- 

 sentially of a pedestal, from which arises a vertical iron shaft 

 carrying a very long horizontal arm, at any point of which 

 the anemometer, to be examined, may be placed, being held 

 firmly by appropriate clamps. The length of this horizontal 

 arm is about seven feet. Its weight and that of the instru- 

 ment are counterbalanced by an adjustable counterpoise, and 

 the whole is made to revolve rapidly for any desired length 

 of time. The vanes of the anemometer, being set in motion 

 by the resistance of the air, record their revolutions electric- 

 ally by appropriate wires upon a chronograph placed con- 

 veniently near to the apparatus. In the formula for the re- 

 duction of the observations, allowance is made for the centrif- 

 ugal force, and for the circumstance that the instrument is 

 in motion while the air is sensibly at rest. So far as the den- 

 sity of the air is concerned, account is taken, not only of the 

 barometric pressure, but of the moisture and temperature, 

 and, apparently, every refinement is introduced into the cal- 

 culations that can be suggested by the most critical mind. 

 The two anemometers upon which observations have been 

 made are those of Robinson and of Negretti & Zambra, or 

 the so-called whirling-machine, the former being the hemi- 

 spheric cup anemometer. As is well known, the former in- 

 strument is now rapidly supplanting all others for the pur- 

 pose of meteorological observations, and it is usually assumed 

 that the velocity of the hemispheric cups, as they revolve in 

 circles about the axis of the instrument, is 0.33 the velocity 

 of the wind. Cavallero's observations show that within the 

 range of his experiments the number 0.36 should replace the 

 value ordinarily assumed, but that it is subject to a compara- 

 tively large change, depending upon the velocity itself; a re- 

 sult that has been remarkably corroborated in the recent in- 

 vestigations of Phillips, in England. Atti della B.Accarf. 

 Scicnze, Turin ^ GG3. 



A UNIVERSAL METEOROGRAPH. 



A very interesting meteorograph, or instrument for record- 

 ing graphically the state of the barometer, thermometer, and 

 with other meteorological features, has been described before 

 the Academy of Sciences, Brussels, by Professor Van Ryssel- 

 bergh ; and the following report concerning its merits has 



E2 



