March 19, 1920] 



SCIENCE 



289 



it is warmer in the anticyclone than in the 

 low. This holds for Europe but is not en- 

 tirely confirmed for the United States. The 

 height of the base of the stratosphere varies 

 in Europe with cyclonic and anticyclonic 

 weather from about 8 to 13 kms. It also 

 varies with latitude, averaging 9.6 at Petro- 

 grad; 10.6 in England; 11 in Italy; and ll.Y 

 in Canada. 



Thus it can readily be predicted that at a 

 height of 10 kms. in the latitude of New York 

 an airman rising on an afternoon in the early 

 fall will experience a temperature lapse or 

 vertical decrease amounting in all to 200 kilo- 

 gxads, i. e., from 1,050 to 850 kilograds, using 

 a scale on which the absence of all molecular 

 heat is represented by and the ordinary 

 freezing point by 1,000. On the Centigrade 

 scale this would be from 14° above freezing to 

 41 degrees below freezing. 



If our atmosphere were homogeneous, we 

 should reach its top at a height of 8,000 

 meters. There would then be no need of 

 superchargers; and oxygen tanks would be 

 advantageous but not absolutely indispensable. 

 But this does not occur in nature and the 

 density of our aerial envelope at 8,000 meters 

 is actually 40 per cent, of what it is at the 

 surface. At 10,000 meters it is just 33 per 

 cent, of the surface density. 



The preceding table somewhat modified 

 from the data given by Dines in his recent 

 paper on the " Characteristics of the Free At- 

 mosphere" indicates the average temperature, 

 pressure, and density of the air at various 

 heights. The height is in kilometers, tem- 

 perature in kilograds, pressure in kilobars and 

 density in grams per cubic meter. 



Schroeder's thermograph indicated a min- 

 imum temperature of — 55 degrees C. (or 99 

 degrees below freezing on the Fahrenheit 

 scale). This on the new temperature scale 

 is 799. It will be seen that this temperature 

 indicates a height of about 11,000 meters. 



In one of Rohlf's ascents he went beyond 

 the top of the troposphere or above what 

 might be called the temperature lid. On 

 that date, the base of the stratosphere was 

 below 10 kilometers and, therefore, he passed 

 into a somewhat warmer level even though at 

 a greater elevation. Alexander McAdie 



Blue Hill Observatort, 



THE SEPARATION OF THE ELEMENT 

 CHLORINE INTO CHLORINE AND 



META-CHLORINE 

 Although many attempts have been made 

 to separate an element into two or more 

 diflerent atomic species, in no case have the 

 experiments met with success. In my opinion 

 this has been due largely to the fact that in 

 all cases where it is Tcnown that isotopes exist, 

 as in the element lead, the conditions imposed 

 upon the experiments by the relative atomic 

 weights of the different atomic species are 

 such as to be extremely difficult to meet. 

 For this reason, when five years ago I decided 

 to make a separation of an element into 

 isotopes, it seemed that it would be easier to 

 separate the isotopes in an element where 

 isotopes were not known to exist, than to meet 

 the extremely arduous conditions of the 

 known cases. 



In 1915 I gave conclusive evidence that 

 chlorine, magnesium, and silicon (in addition 

 to neon as discovered by Thomson), among 

 the light elements, are mixtures of isotopes, 

 and that the atomic weight of the lighter 

 isotope is 35.0 for chlorine, 24.0 for mag- 



