l62 



NA TURE 



[August 4, 1923 



Letters to the Editor. 



\The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, nor to correspond with 

 the writers of rejected manuscripts intended for 

 this or any other part of NATURE. No notice is 

 taken of anonymous communications?^ 



The Mass-spectrum of Copper. 



The number of elements of which the isotopic 

 nature has been determined is now large enough to 

 give considerable weight to statistical relations. 

 Among elements of odd atomic number two definite 

 empirical rules stand out. The first is that none of 

 them consists of more than two isotopes. This has 

 no exception so far. The second is that the more 

 abundant of the two constituents, or both, will be 

 of odd atomic weight. The only exception to this 

 is the element nitrogen ; moreover, the only even 

 isotopes at all are the weaker constituents of lithium 

 and boron. That both of these rules should be 

 violated by copper having the three isotopes 62, 64, 

 66, announced recently by Prof. Dempster, seemed 

 therefore excessively improbable. 



I have now been able to obtain the mass-spectrum 

 of copper by employing cuprous chloride in the 

 accelerated anode ray .method used with the mass- 

 spectrograph. The lines are faint, but their evidence 

 is conclusive since they appear at the expected 

 positions 63 and 65 and have the intensity ratio, 

 about 2.5 to I, predicted from the chemical atomic 

 weight 63.57. The positions of the lines could be 

 determined with great accuracy by comparison with 

 the line 56 due to iron derived from the anode con- 

 tainer. No deviation from the whole number rule 

 was observed. 



With regard to Prof. Dempster's results (Nature, 

 July 7, p. 7), it is very suggestive that the intensity 

 and grouping of the lines he ascribes to copper agree 

 exactly with those of the strong isotopes of zinc. It 

 seems possible, therefore, that they are due to the 

 presence of traces of that element either in the 

 copper or more probably, together with the rubidium 

 he mentions, in the furnace material. 



F. W. Aston. 



Cavendish Laboratory, Cambridge, July 25. 



Polar Temperatures and Goal Measures. 



For some years I have held a view of the possible 

 origin of some at least of the coal measures of the 

 polar regions that is not found in the ordinary^ 

 geological text-books. After discussing it with a 

 dozen friends who are geologists, and some of them 

 specialists in glacial geology, I have concluded — 

 somewhat to my surprise — that the theory is new. 

 A short statement of the theory may therefore be 

 desirable. 



It is generally considered that certain plants are 

 not limited in their geographic range, by no matter 

 how intense a cold in winter, if only they have an 

 adequately hot summer. Apparently this hot summer 

 may be very short and still the^ plants prosper. 

 Notable examples are the black spruce of northern 

 Canada and similar trees in the northern part of the 

 Old World. 



In the western hemisphere I have examined 

 specimens of coal from 79° north latitude. So far 

 as the material could be identified it was coniferous. 

 In other deposits almost equally far north I have 

 found gum and pine cones. 



The northern limit of conifers in North America 

 at present is between 68° and 69° north latitude. 



NO. 2805, VOL. 112] 



That this limit is determined not by intensity of 

 cold in winter, but by lack of heat in summer, is 

 shown by the luxuriance of the black spruce and 

 several other trees in the mountain valleys of the 

 Yukon, where the minimum temp>craturcs in winter 

 are from 10° to 20" lower than at the northern limit 

 of trees. This northern limit is therefore deter- 

 mined by the proximity of the Arctic waters chillc' 

 by floating ice, which lower the summer temperatui 



The United States Weather Bureau frequentl> 

 reports temperatures above 90 '^ in the shade, observed 

 under standard weather bureau conditions, at Fort 

 Yukon in Alaska, just north of the Arctic circl 

 The Bureau occasionally reports 95° F., and ha^ 

 reported even 100° F. The Canadian Weather 

 Bureau reports nothing above 88° F., but that is 

 because its northern stations are strung out at intervals 

 along the northward flowing Mackenzie River. On 

 two journeys down this river (1906 and 1908), and 

 from common report as well as from weather bureau 

 observations, I know that there is on most occasions 

 a wind blowing with almost the steadiness of a trade 

 up the Mackenzie valley from the Polar Ocean 

 Explorers who have been in the Canadian Arcti' 

 away from the Mackenzie wind-trough, have observe* 1 

 temperatures much higher than those recorded b\ 

 the Weather Bureau. 



We have, then, observational confirmation of the 

 theory, according to which the polar regions receive- 

 about as much heat for five weeks in summer ;. 

 does the equator. 



Most observers reporting climate from the polar 

 regions have done so from locations on shipboard 

 or on a sea-coast, where the downpour of the summer 

 sun's heat has been neutralised by the chill of the 

 ocean stored up through a long and cold winter. 

 It is true that the ground in the Arctic is frozen, 

 and that the temperature of the earth 40 or 50 ft. 

 down has been found to be about -i-io° F., whereas 

 the ocean 50 ft. down would have a temperature 

 about -f29° F. Soil and even rock are, however, 

 poor conductors of heat, and the ground chUl is 

 imprisoned, while the ocean chill is freely liberated. 

 Furthermore, the great heat of summer produces on 

 most land surfaces a mat of vegetation, which is an 

 even poorer conductor of heat than the earth itself. 

 This is why a thermometer 6 ft. above a damp 

 meadow in the arctic regions of Alaska, protected 

 from the sun's rays in the usual weather bureau way, 

 is able to record temperatures ranging from 60° F. 

 to 100° F. almost every day for a period of several 

 weeks in midsummer. 



Consider now what the weather conditions in the 

 Arctic Regions would be if, instead of the present 

 ocean ranging in depth from one to three miles, we 

 had an extensive low land — say a continent as low 

 and as flat as Australia, with the North Pole near 

 the centre of it. Better still, assume that the low 

 land of northern Siberia, with physical characteristics 

 such as it now has, were to extend to and beyond 

 the North Pole, including a large part of the Canadian 

 Archipelago, or even joining up with North America 

 itself. Remembering that the sun delivers about as 

 much heat in the Polar Regions as in the Tropics 

 in midsummer, and also the observation that frozen 

 ground has little effect upon the temperature of the 

 air above it, then according to recorded midsummer 

 lowland temperatures at present in the Polar Regions, 

 we should have at the North Pole July heat of 

 so-called " tropical " intensity, and conditions all 

 over the Arctic suitable for dense forests of black 

 spruce and other trees and shrubs, without calling 

 upon any further alteration in environment — such 

 as different chemical composition of the atmosphere. 



