bbb 3, tgi8 



NATURE 



97 



icilies up to - 

 - 



h ing dynamometrii instrumei 

 magnetically shielded and a i 



I '< i ■ ■ h compl 51 



■ lb. 



auf, Augusi 

 po'wden d 

 insensitive to moisture. Fineh ground and 

 well-dried coal 1 powdei is mixed with fineh 



divided powdered peat, which, before grinding, 

 artificialh ai nol less than 100 ' 



OUR ASTRONOMICAL COLUMN. 

 Observations 01 Solar Prominknchs. \ sunn 

 of the observations of prominences made at Kodai- 

 kanal during thi second hall ol thi year 1917 is given 

 bj M in Bulletin No. 58. Thi 



frequi height, and mean extern along the 



sun's limb were respectively 200, ,;.V. and ;.s s • 

 ring hut little from the corresponding figures foi 

 the firsi half of the year. Then were three principal 

 ictiviti : one aboui the equator, a mid- 

 latitudi .'nn. between I jo and 40 , and a high- 

 latitude aone betwe n 70 More than hall 

 hi nineteen metallic prori wen 

 ■ il during December, which was also the mosi 

 month magnetically, in observations on the 

 hi sun, 239 bright 1 ersats of IL and 

 eighteen dark reversals of I) wen noted, and photo- 

 graphs of II,. absorption markings were obtained on 

 1 1~ days lh' areas and numbers of the absorption 



markings showed .1 targ on the previous 



increase in the densitj 1 if tin 

 prominences excepl in thi c; ol thosi occurring 

 about latitude 6o°, which have seldom given evid 

 of their presence on the disc. The distribution of the 

 markings showed the usual excess on tin eastern 



I). tails of the observatkw - nences made at 



.1 during mil' Id been published b\ 



Prof. \. Ricc6 {Mem. Soc. Sp'ett. Ital., vol. vii", 

 si 1 i. - a) rhi mean daili number of prominences 

 hi ighl \>i . and the mean 1 xtent of 

 basi 1 was a considerable increase in the 



frequency a- compared with 1015. 



Parallaxes or Helium Sim.- I h. recent deter- 

 minations at Greenwich of the proper motions "I stars 

 down to o'li magnitude in the | ti have 



utilised b\ Sir 1- . Dyson and Mr. \V. 'i. 

 Thackeraj in an investigation of the paralla es and 

 intrinsic magnitudes "I somi ■ B (helium) stars 



thi; Notices, R. \.s . vol. Ixxviii., p. 651). The 

 died is that portion ol the galaw intercepted 

 by thi > een -)h. and R.A. The stars 



near 6h. have a la ii I ctor almost wholh 



lination, and on the assumptioa that they have 

 no 91 • il due to thi 



ii in parall ixes ol I ; stars of diffi 1 1 m 

 magnitudes ran t> H3 stai • ol tvpes 



I'.s nd B 1. ranging in mean appan nt magnitude from 

 r-78 to 8-46, the mean propei mi ions in declination 

 fi 1 .in n 1 --. 6", the mean parallaxes 



from 0-05" i" 0-02", and the intrinsii magnitudes 



ding with the parallax o-l from +04 to 0-5. 



^.tension of the invi o faint stai - thus 



confirms the view that stars ol - B8 and Bq have 



riosity . \ similai 



: : 



mi.,,- .-' 1 - anging 



from 4-o-q to -i-is for magni- 



iL. I02 n 



1 I Mis. -A 



on "To vlean Di , i ., i 



tral I Hirayan in the 



Annalt app< ndix 7. 



riie purposi of the autl - pteyn's formulae 



parallax with its magnitude, - 

 tral tj |i'-, and propi : stars, foi 



which both measui ed and illaxi - - 11 ' 



1- the lattei 31 1 v anti pes A and 



B, he uses van Rhijn's for them. Far 



stars "I magnitude 4-8 he finds th 



foi type M ; as the t) pe ch . ■ \l 



through K to G„ it rises steadil; to a maximum of 

 0-054", and then falls again as we pass througl 



F and A, being 8" Foi type 11. Hi- valui 



with those of Kapteyn for types B, and A , but for 

 the remaining types the\ are aboui twio as | 



ENTOMOLOGICAL RESEARCH IN 

 1/ ST R ALIA. 



MR. R. J. TILLVARD, whose admirable book on 

 "The Biology of Dragonflies" was recently 

 reviewed in Nature, has made a further contribution 

 of importance to the study of this order of insects 

 in a series of papers on "The Morpholog) ol the 

 Caudal Gills of the Larva? of Zygopterid Dragon- 

 flies, ' published in the Proceedings of the Linnean 

 S01 iet) of New South Wales (vol. xlii., n.17, parts 

 1 and 3). Zygopterids are the slender-bodied dragon- 

 flies, often distinguished as "demoiselles," the larvae 

 and n\ mphs of which are provided with three conspicuous 

 appendages, at the hinder end of the body, traversed 

 b} branching air-tubes. A careful comparative study 

 of the structure of these organs in various genera 

 and in successive stages of growth has been man 

 the author, who concludes that the median dorsal 

 gill-plat.- in these insects is analogous with the telson 

 in Crustacea, while the paired lateral appendages are 

 cerci, and " therefore the true homologues of the 

 uropods of Crustacea." The-, latter are compared 

 with the filamentous cerci of the well-known stonefty 

 (Perlid) larvae and nymphs, which the; resemble in 

 form in the early stages, becoming more highly 

 specialised .1- growth proceeds. From his comp 

 tive studies Mr. Tillyard is convinced that in Che 

 evolution of this group of dragonflies a primitive 

 filamentous condition of the larval telson and cerci 

 was succeeded bi thi "saccoid" type, which persists in 

 a few genera such as Diphlebia and Neosticta,* this by 

 the " triquetro-quadrati " type, found in the Caloptery- 

 ginas, where the median gill is trapezoidal and the 

 lateral ones are triangular in croi — iection, and this bj 

 the specialised "lamellar" typi characteristic of thi 

 larvae oi thi greal majorit; ol the group, including 

 the familiar Agrioninae. The author promises further 

 studies on the phvsiolog; oi these interesting - 

 tures, for although their function is doubtless respira- 

 tory, the aquatii larvae which possess them continue 

 eathi n ■■ 1 wa\ w hen artificially depi ived 

 of them. 



The r. in. irk , ii -I insect-fauna of the Australian 

 region has provided material in other orders foi Mr. 

 Tillvard's resi trches. In Tasmania, New South 

 Wales, and New Zealand he has discovered various 

 ,1, [,i. ,ti_ili,--. (Mecoptei a), whii 

 11 Linn. Soc, \.S.\\'.. vol. xlii., 

 ,,, i - , epn senting a new familj 1 N 



,vith the jaws apparentlv piercing and sm 



irallel to ii idition i- 1 : in many 



ni combining remarkabl with 



1 mian and 



- Ni v Soutl " ■ pai I 41 



Mr. Tillvard lescrib extim 



