220 PROGRESS OF METEOROLOGY IN 1889. 



Aspiration thermometer. — Professor Assmanu has replied to the objec- 

 tions wliich have beeu raised against Lis aspiration thermometer, alter 

 giving- it a thorough test. The instrument, even when exposed to the 

 most intense sohir radiation, should record the true temperature of the 

 surrounding air. In order to determine whether the instrument satis- 

 fies this requirement, Dr. Assmann spent four weeks on the Sentis and 

 found as a result of several thousand observations that this condition 

 is fulfilled by the instiument in its present form. By means of an ar- 

 rangement of clock-work, a constant current of air is drawn through the 

 metallic tube which surrounds the thermometer. This clock-work 

 is attached to the upper end of the tube and drives a fan with consid- 

 erable velocity, thus forcing the air out of the tube at the top and draw- 

 ing it up from the lower portion of the tube ; by this means a rapid 

 current of air is kept streaming over the thermometer. By direct ex- 

 periment with hot water he found that the temperature is not aft'ected 

 even when the temperature of the metal tube is 20° C. above that of 

 the surroundiug air. (Nature, XL, p. 660.) 



New hygrometer. — H. Dufour has constructed a dew-point hygrometer, 

 the peculiarity of which is that the condensing surface, instead of 

 being a thin silver plate, is a thick silvered copper plate with the ther- 

 mometer embedded in it. The thermometer thus set is supposed to 

 register the temperature of the condensing surface more accurately than 

 when immersed in the evaporating liquid, and that one of the largest 

 errors incident to the dew-point hygrometer is thereby overcome; but 

 it seems questionable whether this result is secured. {Bull. 8oc. Vau- 

 doise, 1888, p. 88.) 



The Tenth Anriual Exhibition of Instruments by the Eoyal Meteoro- 

 logical Society was held March 19-22, 1889. Special attention was given 

 to the display of all forms of solar radiation apparatus. There were 

 shown specimens of the actinometer of Sir John Herschel, that of Hodg- 

 kinson, Pouillet's direct pyr-heliometer, Secchi's apparatus, Balfour 

 Stewart's actinometer, black and bright bulb thermometers in vacuo, 

 Luvini's di-etheroscope, Bellani's lucimeter, Crooke's radiometer, sun- 

 shine recorders, and photometers. 



Among new instruments exhibited wereFineman's and Galton's nepho- 

 scopes, Davis's improved air meter, Negretti and Zambra's recordiug 

 hygrometer, and de Normanville's self-compensating sympiesometer. 



Mr. Clayden showed a working model illustrating the generation of 

 ocean currents. This shows how the prevalent winds over the Atlantic 

 are the chief cause of the circulations of the waters. A number of tubes 

 are so arranged that when an attached blower is worked the circulation 

 of air produced resembles that of the atmosphere ; the imitation winds 

 thus set up, re-act upon the surface of the water, creating a system of 

 currents which reproduces the main features observed in the Atlantic. 



