PKOGRESS OF METEOROLOGY IN 1889. 221 



Mr. Claydeu also showed some lantern slides illiistratiug the spiral 

 circulation of the wind both in a cyclone and an anti-cyclone. 



Mr. A. L. Kotch describes the meteorological instruments exhibited at 

 the Paris Exposition, the special features of which are tlie many novel- 

 ties presented in self-recording apparatus. {Am. Meteor. Journal, vr, 

 pp. 293, 362.) 



Professor Tait has devised an instrument, named the stei)lianoii]e, for 

 measuring the angular size of halos, parhelia, corona', etc. It is now 

 used at the Ben Nevis Observatory. 



Cloud Photography. — Dr. Riggenbach, of Basle, has adopted special 

 methods for overcoming the dil3iculties met in photographing cirrus 

 clouds. The blue light of the sky acts with nearly the same active 

 energy as the white light of the clouds. Dr. Riggenbach dulls tlie blue 

 light of the sky by means of the analyzer of a })olarizing apparatus. 

 The blue sky-light is partly polarized, and to the largest extent at the 

 points which are situated 90^ from the sun ; tlie plane of polarization 

 passing through the points looked at, the sun, and the eye of the ob- 

 server. Ou the other hand, the light from a cloud is [)olarized only to 

 a slight extent. Instead of a NicoPs prism, a dark mirror, or better, a 

 plate of obsidian may be used; and, when conveniently situated, the 

 surface of a lake may be used as a polarizing mirror. {Nature, xxxix, p. 

 112.) 



Thermometer Shelters. — In vol. X of Aus dcm Archiv der Deutschen See- 

 icarte, Dr. Kop[)en contributes a useful paper on the determination of 

 air temperature. The author investigates the influence of radiation on 

 different thermometers and screens, and gives a resum6 of the experi- 

 ments with regard to the latter in various countries, and of the obser- 

 vations on local differences of temperature (including the intlueuce of 

 radiation). These experiments seem to show that screens through 

 which the air can pass freely, are better than large shelters, and that the 

 effect of radiation is lessened by the free circulation of the air, and b}'^ 

 the smallness of the thermometer bulbs. 



Psychrometry. — Dr. Grossmann has published in the Meteorologische 

 Zeitschrift an elaborate paper on the theory of the psychrometer, with 

 an introductory sketch of the development of the subject up to the 

 present time. The following is an outline of his treatment: 



(1) If a wet bulb exposed in air (pressure B, vapor pressure p, and 

 temperature t) reads ^i in consequence of the evaporation of water (the 

 latent heat being A), and if pi be the pressure of saturated vapor at ti, 

 we may assume that, when the conditions have become steady, the 

 process which has gone on and is going on continuously round the wet 

 bulb is as follows: A quantity of heat is absorbed by evaporation, the 

 vapor pressure of a layer of air containing wj, grams of dry air being 

 raised from p to p^; this heat is supplied by the reduction of the tem- 

 perature of a layer of air, containing m' grams of dry air, from t to ^i. 



Equating these quantities of heat, we get, if S be the specific heat 



