8o 



NATURE 



[September i6, 1915 



spectral type separately (except only the A stars), and 

 the effect appears to be more marked in the later 

 types. Further, the highest known velocities are 

 found in the vicinity of the Milky Way. It is con- 

 jectured that the effect may be due to the operation 

 of a resisting medium on stellar bodies differing in 

 size and density, or the closer proximity of the fainter 

 stars to a "source of general gravitational action." In 

 either case the Milky Way would be deeply concerned. 

 In another note in the same journal Mr. Perrine 

 analyses the spectral distribution of the stars of large 

 radial velocity, finding the maximum mean values 

 among the faint stars of classes F and G, 



Volcanic Dust Veils and Climatic Variations. — 

 Fluctuations in the observed intensity of the solar radia- 

 tign have been interpreted during the past ten years or 

 so as traceable to the screening effects of the enormous 

 quantities of dust poured into the upper atmosphere 

 during notable volcanic eruptions ; thus it has been a 

 small step to the wider hypothesis that volcanic dust 

 has been a possibly important factor in the production of 

 past climatic changes. This hypothesis is tested by 

 Mr. Henryk Arctovvski in a paper communicated to 

 the New York Academy of Sciences (Ann., Vol. xxvi., 

 pp. 149-174, June, 19 15). Previous work on tempera- 

 ture records had led him to the conclusion that a 

 general rise in the temperature of the atmosphere was 

 probably due to an increase in the solar constant itself. 

 From a re-examination of temperature curves, chiefly 

 showing departures from monthly means, paying 

 special attention to the epochs of the Krakatoa (1883) 

 and Katmai (19 12) eruptions, as well as the year 

 1902, which was marked by intense vulcanism in both 

 hemispheres, he now concludes that the ^hort-period 

 variations of temperature have nothing in common 

 with the presence or absence of volcanic dust veils, 

 although minor secondary modifications of the tem- 

 perature curve may sometimes be traced to this cause. 

 He finds that the sun-spot variation does appear to 

 have an influence on atmospheric temperature, and, 

 moreover, presumes, but does not explain, the exist- 

 ence of a correlation between the temperature changes 

 and frequency of volcanic eruptions. 



The Aurora Borealis.— An illustrated account was 

 given in Nature, August 7, 1913, of the photographic 

 observations made by Prof. Carl Stormer, in collabora- 

 tion with M. Bernt I. Birkeland, in the spring of 

 1913. These observers were stationed at Bossekop 

 and Store Korsnes respectively. They secured a great 

 \yealth of parallax material which will require a long 

 tirne for reduction. However, one-sixth having been 

 finished. Prof. Stormer has published a preliminary 

 report (" Terres. Mag. and Atmos. Elec," vol. xx". 

 No. i). Some six hundred measures of altitude have 

 been worked out, most of the measured points lying 

 between 90 and 130 km. above the earth's surface; 

 none come out appreciably lower than 90 km., whilst 

 the highest reaches 230 km. From a mere inspection 

 of the diagram the mean height appears to be about 

 120 km. ; thus the lower limit is fairly well marked. 

 The spatial relations of a number of auroral curtains 

 have been worked out in detail. In one case this 

 information has been used in conjunction with mag- 

 netograms from the Haldde Observatory, to obtain an 

 idea of the nature of the aurora. The curves show 

 that the magnetic effect due to the passage of the 

 particular auroral feature had components directed 

 N.W. and upwards. On the assumption that the dis- 

 play was caused by electric corpuscles travelling 

 towards the earth. Ampere's rule indicates that the 

 observed deflections would result from the motion of 

 particles carrying a positive charge. 

 NO. 2394, VOL. 96] 



AMERICAN HYDROIDS.^ 

 jV/TR. NUTTING may be congratulated on the com- 

 ■*•*•*- pletion of the third part of his great monograph 

 on American Hydroids. He has a generous concep- 

 tion of America, and includes in his list such species 

 as Silicularia hemispherica from S. Tierra del Fuego 

 and 5. repens from Kerguelen. It is therefore almost 

 a monograph of the hydroids of the world, and will be 

 regarded as the most important work of reference on 

 the group that has yet been published. Those who are 

 specially interested in Ccelenterata will probably be 

 gratified to find that Mr. Nutting has taken a con- 

 servative attitude as regards species, and that, not- 

 withstanding the many temptations to which he has 

 been exposed in the course of his vast labour in this 

 field, he has added very few new species to those 

 already recognised. It is a much easier method — and 

 a particularly attractive one in the preparation of a 

 standard treatise on systematic zoology — to make new 

 species when difficulties arise than to exercise the 

 skill and patience that is required to place doubtful 

 specimens in their proper specific groups, and we may 

 regard it as a sign of Mr. Nutting's knowledge and 

 thoroughness that the list of species is not a longer 

 one. 



The method adopted in dealing with the species is 

 to select a specimen regarded by the author as typical, 

 to give in a footnote the locality from which the speci- 

 ment came, and then to describe it in detail. There 

 is much to be said for this method in dealing with the 

 systematics of Ccelenterata, because it gives the 

 systematist a fixed point, as it were, around which the 

 variants may be grouped, but it seems to us that to 

 that description of a type some statement should be 

 added of the principal variations observed by the author 

 in the species under consideration in order that future 

 workers in the group may find that some of the diffi- 

 culties they are sure to meet with in using the mono- 

 graph as a standard work of reference have been 

 anticipated by a recognised authority. 



The author has evidently taken infinite pains to 

 collect from all available sources specimens of 

 American hydroids for study and description, and his 

 reference lists at the head of each species are extra- 

 ordinarily complete and accurate. Our thanks are due 

 to him for a very valuable work. S. J. H. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



The Board of Education informs us that the regu- 

 lations and syllabuses which governed the examina- 

 tions in science and technology held in 1915 will con- 

 tinue in force for 19 16. In the prefatory note to the 

 volume of regulations and syllabuses for examinations 

 in science and technology, 1915, the Board announced 

 its intention to discontinue those examinations at a 

 date to be afterwards announced. The Board now 

 gives notice that after 1916 it will no longer hold 

 lower general examinations in any subjects of science 

 and technology. The higher general examinations 

 will for the present be continued. 



The prospectus for the forthcoming session of the 

 Belfast Technical Institute has now been published. 

 An Interesting departure is the indication by an 

 asterisk prefixed to the name of the members of the 

 permanent staff who are at present serving in the 

 Army or Navy, or who are engaged on war service. 

 The number of asterisks is excellent testimony to the 



1 "American Hydroids." Part III. The Camranularidae and the 

 Bonnevielltd'se. Smithsonian Institution. Special Bulletin. Pp. 126 + 70 

 text figures+27 plates. Washington, 1915. 



