September 29, 1923] 



NA TURE 



473 



He suggests that such winds would be even more 

 persistent in the hypothetical southern continent. 

 In that connexion we must remember that in spite of 

 the northern cold summer monsoon the Mackenzie 

 coniferous forest does extend more than 150 miles 

 north of the Arctic circle, and indeed north of the 

 southern limit of the maximum " tides " in the 

 Mackenzie (by tide we here mean the rise of five or 

 six feet in the eastern Beaufort Sea caused occasion- 



fally by westerly gales. The tide, proper, is less than 



[one foot). 



No such extremes as the occasional Arctic +95° F. 



fare necessary for the prosperity of conifers. Mr. 

 Elihu Stewart, the Forestry Commissioner of Canada, 

 put on record in the publications of his department 

 {in 1907 or 1908) that he had seen trees 100 feet 

 high more than 100 miles north of the Arctic circle 

 in the Mackenzie delta. Trees above 75 feet in height 

 abound forty or fifty miles farther north. I do not 

 know of any systematic temperature observations 

 taken in the Mackenzie delta at the approximate 

 northern limit of the conifers, but I suppose that 

 70° F. in the shade is there exceedingly rare. I 

 should judge then that any hypothetical conditions 

 in the Antarctic considered adequate to produce 

 maximum temperatures of 75° F. (even though rarely) 

 -would give an adequate heat factor for coniferous 

 forests. ViLHjALMUR Stefansson. 



New Court, Middle Temple, E.C.4, 

 September 5. 



Can the Geostrophic Term account for the 

 Angular Momentum of a Cyclone ? 



In meteorological discussion it is sometimes implied 

 that the rotative velocity of the air comprising a 

 cyclone is primarily accounted for by the geostrophic 

 term in the equation of motion. 



If considerations of a second order of magnitude 

 "be ignored this hypothesis is capable of simple 

 treatment in its main features and is worth examina- 

 tion. Imagine an initial circulation round an axis, 

 of any magnitude whatever, and consider an elemental 

 mass 5m at distance r from the axis. 



The radial velocity of this element is then denoted 

 "by dYldt taken positive outwards. 



The increase in the angular momentum of 5m 

 about the axis in time 5/ due to the geostrophic 

 term is 



2w sin <t> .r . Sm . St ,-, 

 at 



taken positive clockwise in the Northern Hemisphere. 



In the limit this becomes w sin <i> . dm{2r . dr), or 

 «sin <l> . d{r^ . Sm). 



If <f> be taken as constant, and we sum up for the 

 whole mass of the cyclone, we see that the increase 

 in the total angular momentum in a given time is 

 equal to the product of w sin <(> into the corresponding 

 increment in the moment of inertia about the axis. 



The extent to which the moment of inertia can 

 vary is represented by the deepening or filling up 

 of the cyclone, and a rough calculation shows that 

 the possible angular momentum so accounted for is 

 'very small, and is, moreover, of the opposite sign to 

 that required by the hypothesis under consideration. 



In the above analysis two things have been ignored : 

 (i) The question of the variability of </> ; (2) the resist- 

 ance of the earth's surface. If it be supposed that 

 thefe is a systematic difference between the latitude 

 of the surface inflow and that of the outflow above, 

 there is the possibility of the existence of a term of 

 appreciable magnitude in the case of a large cyclone. 

 On this point observational evidence is weak, and 

 all that can be said is that for a small system the 



effect must be small, and for large ones we have no 

 reason to suppose it to be large. 



The resistance of the earth's surface continually 

 tends to reduce the rotational velocity, and the 

 magnitude of the term concerned is, moreover, large 

 compared with (i), which is of the nature of a 

 differential effect. 



On the whole, it seems clear that the angular 

 momentum of a rotating system cannot be accounted 

 for by the geostrophic term, and that its origin must 

 be sought in the initial relative velocities of masses 

 of air subsequently included in the circulation. 



L. H. G. Dines. 



Benson, Wallingford, August 31. 



Zoological Nomenclature : Spirifer and 

 Sy ringothyris . 



In accordance with prescribed routine, the Secretary 

 of the International Commission of Zoological Nomen- 

 clature has the honour herewith to notify the members 

 of the zoological profession that Miss Helen M. Muir 

 Wood, of the British Museum of Natural History, has 

 submitted the generic names Spirifer, Sow, 18 16, and 

 Syringothyris, Winchell, 1863, to the International 

 Commission, for suspension of rules, with the view of 

 retaining Anomia striata Martin as genotype of 

 Spirifer, and Syringothyris typa (s. Spirifer carteri 

 Hall) as genotype of Syringothyris. 



The argument is presented : (i) that under the 

 rules Anomia cuspidata Martin is type of Spirifer, and 

 Syringothyris is synonym of Spirifer : (2) but for 

 seventy years, practically all authors have, in con- 

 scious opposition to the rules, taken A . striata as type 

 of Spirifer, and Spirifer carteri ?>. Sy. typa as type of 

 Syringothyris : (3) so many species are involved in 

 this instance that the application of the rules would 

 present greater confusion than uniformity. 



The secretary will postpone vote on this case for 

 one year, and invites expression of opinion for or 

 against suspension in the premises. 



C. W. Stiles, 

 Secretary. 



Hygienic Laboratory, Washington, D.C. 



NO. 2813, VOL. I 12] 



Colour Vision and Colour Vision Theories. 



Prof. Peddie states in his letter in Nature of 

 September 8, p. 362, that the facts that I have given 

 as totally opposed to the trichromatic theory can be 

 explained by it. If he will show how this can be 

 done I can then deal with his explanations. Directly 

 the trichromatic theory is put in a definite form its 

 failure becomes evident. For example, it has been 

 stated frequently by others that the construction of 

 the trichromatic theory given to explain simultaneous 

 and successive contrast will not explain colour blind- 

 ness, and vice versa. There is no fact that directly 

 supports the trichromatic theory. In numerous cases 

 papers written to support the trichromatic theory 

 are found on examination to give facts strongly ad- 

 verse to it. Prof. Frank Allen has written a number 

 of papers supporting the trichromatic theory. In 

 a paper on the Primary Colour Sensations {Philo- 

 sophical Magazine, vol. xxxviii., July 1919, p. 81) 

 Prof. Allen writes : " But it is difficult to understand 

 why the exceedingly complex region between X*47o n 

 and X-^jOfi should exhibit, as it does, persistency 

 curves with only one elevation in the green." The 

 reader should note that it is only on the trichromatic 

 theory that this region is complex. On my theory it 

 is quite simple and the results should be as stated. 



F. W. Edridge-Green. 



London, September 10. 



N 2 



