528 



SCIENCE 



[N. S. Vol. XXXIV. No. 877 



sine flexure and A<p are as follows. The signs have 

 been changed for sub-polars. 



In addition to the above observations there are 

 about 2,500 made by Mr. Geo. A. Hill and Mr. H. 

 B. Evans from 1898 to 1903, which are nearly 

 reduced. A preliminary survey indicates the fol- 

 lowing relative personal equations for declinations 

 of the south stars: 



H-L = — 0".2, 

 E-Lr=— 0".4. 



Some experimental work to clear up this matter 

 will be undertaken before combining these ob- 

 servations into a catalogue. 



The Earth's Radiation Zones: W. J. Humphreys. 



(Read by Professor Eichelberger.) 



Since heat may be transferred from one object 

 to another only by conduction, convection or radia- 

 tion, therefore by measuring the temperature of 

 the isothermal region of the atmosphere, in which 

 both conduction and convection are small, it is 

 possible to determine the radiation intensity of 

 the earth at as many places as one may wish. 



The effective radiating level, as determined by 

 Abbot and Fowle, has an average elevation of 

 about 4 kilometers, consequently the lower clouds 

 are within the radiating surface while the cirri 

 are above it. Hence the latter, and they alone, 

 can strongly affect the intensity of the outgoing 

 radiation. 



An extensive exploration of the upper atmos- 

 phere with sounding balloons has shown that, prob- 

 ably because of the unequal distribution of cirri, 

 the intensity of the earth 's escaping radiation 

 within the tropics is to that of latitudes 35° to 

 60°approximately as 3 to 4. In fact, as a radi- 

 ator the earth has an inefS.cient equatorial zone, 

 efficient zones of middle latitudes, and finally, for 

 which there is some evidence, inefficient polar caps. 



The Amount and Vertical Distribution of Water 



Vapor on Clear Days: W. J. Humphreys. 



(Eead by Professor Eichelberger.) 



It is important to any one using a bolometer, 

 or a pyi'heliometer, to know the approximate 

 amount of water vapor through which the radia- 

 tion reaching his instrument has passed. In at- 

 tempting to determine this amount the records 

 have been brought together of 74 balloon flights, 

 made on cloudless days, or such as were adapted 

 to the ordinary use of the bolometer. 



According to these data the amount of water 

 vapor per unit volume decreases with elevation on 

 cloudless days in an approximate geometric ratio, 



and the thickness of the water layer that would 

 result from a condensation of all the water vapor 

 in the atmosphere on such days above any given 

 level may be approximately expressed by the 

 equation 



d=:2e, 



in which d is the depth of the water layer in milli- 

 meters, and e the partial pressure of the water 

 vapor, at the place of observation, in millimeters 

 of mercury. This value is about 13 per cent, less 

 than that given by Hann for all sorts of days, and 

 heretofore commonly used in bolometric work. 



Daytime Laboratory Work in Astronomy : Sarah 



P. Whiting. 



The list of members of this society includes 

 those responsible for the teaching of astronomy 

 in more than fifty colleges and universities. It 

 seems therefore in order that the society should 

 take cognizance not only of the research work by 

 which knowledge is increased, but also of the 

 teaching by which it is diffused. 



Prom not very detailed information it seems 

 probable that the methods of teaching generally 

 used in elementary classes are not those of the 

 other sciences. 



Daytime laboratory work in astronomy by the 

 students themselves requires a teaching force, an 

 equipment of instruments and photographs, and a 

 place for the work, which has not yet been de- 

 manded by the departments of astronomy nor 

 provided by the institutions. No less research 

 work should be done by the observatories, but the 

 teaching should not be allowed to suffer. Useful 

 apparatus and photographs which are the material 

 for daytime work will never be provided by deal- 

 ers in apparatus till a sufficient number of institu- 

 tions adopt modern methods of teaching to make 

 a demand for such material. Also larger numbers 

 of students should take an elementary course in 

 astronomy to lessen the deplorable ignorance 

 which exists. 



Other learned scientific societies have lent val- 

 uable aid to the advancement of elementary teach- 

 ing. May it not be for the advancement of astron- 

 omy for this society to consider the teaching of 

 those beginning classes from which the profes- 

 sional astronomers and the patrons of the observa- 

 tories must come? 

 On Scales of Intensity for the Lines of the Solar 



Spectrum: Prank W. Very. (Eead by Mr. 



De Lury.) 



A spectral line not appreciably broader than an 

 image of the slit, and perfectly black, may be 



