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NATURE 



[April 22, 1922 



A Unique Long-period Variable Star. 



By Major W. J. S. Lockyer. 



SINCE the year 1811 the star designated R. 

 Aquarii (position for 1900 Right Ascension 

 23i» sS-e"", Declination - 15° 50') has been known as 

 a variable star. It goes through a complete cycle of 

 variability in 385-5 days, attaining a maximum 

 brightness of 6-2 and a minimum of ii-o. 



This star, like about 85 per cent, of all long-period 

 variables, has a spectrum of the class Md, i.e. a 



Fig. I. — Nebulosity around R. Aquarii. 

 Photographed by C. O. Lampland, Lowell Observatory. 



spectrum showing bright hydrogen lines and numerous 

 absorption flutings of titanium-oxide on a continuous 

 spectrum, and indicative of comparatively low tem- 

 perature. 



On October 16, 1919, Mr. Paul W. Merrill, using 

 the 100-inch reflecting telescope of the Mount Wilson 

 Observatory, discovered that several other bright 

 lines, characteristic of gaseous nebulae, were present. 

 This made the spectrum unique, because while there 

 is considerable evidence to connect hot stars, such 



as Class O or Wolf-Rayet Stars, with gaseous nebulae, 

 there was no instance, prior to this, in which a 

 comparatively cool star is associated with the nebulae. 



A further interesting observation that has been 

 made is that while the nebular lines remain almost 

 constant in intensity throughout the light changes 

 of the star, the other lines representing the Md 

 spectrum vary through a large range. This suggests 

 that the star and nebula are independent of one 

 another : other observations on the other hand tend 

 to show a close connection between the two. 



The most recent discovery relating to this star is 

 of extreme importance, for it is now known that the 

 star is in the centre of a m'ass of nebulous matter. 



The photograph showing this was taken by Mr. 

 C. O. Lampland with the 40-inch reflecting telescope 

 of the Lowell Observatory. This nebular image he 

 describes as an oval-shaped, elongated configuration 

 composed of arcs of well-defined nebular filaments 

 and the star is centrally and symmetrically placed. 

 The position-angle of the longer axis of the formation 

 is about 90° and the greatest extent of the faint 

 structure in this direction is a little more than two 

 minutes of arc. Mr. Lampland has forwarded a 

 positive photograph on film from which the ac- 

 companying illustration (enlarged twice) has been 

 made. On his photograph i mm. represented 24-5 

 seconds of arc (approx.). 



The general form of the nebulosity here displayed 

 is very similar to that of the nebula N.G.C. 5921. 

 This latter is reproduced on Plate I. in vol, xiii. of 

 the " Pubh cations of the Lick Observatory," and is 

 given there as an example of what Mr. H. D. Curtis 

 calls a ^-Type Spiral Nebula. 



The actual presence of this nebulosity is of great 

 value in accounting for the unique character of the 

 star's spectrum. Attention must also be directed to 

 the importance of long -exposed photographs with 

 powerful reflectors for the purpose of searching for 

 nebulosities whenever nebular lines appear in a 

 spectrum. It will be remembered how such lines, 

 appearing in the spectra of novae in the later stages 

 of their career, led to the discovery of the presence 

 of nebular matter surrounding the star. 



Marine Invertebrates. 



FURTHER reports on material collected by the 

 British and Australian Antarctic Expeditions 

 have been received. The Chaetognatha of the 

 Australian Expedition have been described by 

 Prof. T. H. Johnston and Mr. B. B. Taylor, 

 systematic accounts of the Crustacea of the British 

 {Terra Nova) Expedition are given by Mr. R. W. 

 Barney on the Ostracoda, and on the Tanaidacea 

 and Isopoda by Dr. W. M. Tattersall. Dr. H. M. 

 Woodcock and Miss Olive Lodge describe the collec- 

 tion of parasitic protozoa, which consists of only 

 three species — a new species of the flagellate genus 

 Cryptobia, a new species of Gregarine (Selenidium), 

 and a ciliate. This ciliate, for which a new genus 

 (Haematophagus) is created in the family Stentoridae, 

 is parasitic on the baleen plates of the humpback 

 whale, and feeds exclusively on the whale's red- 

 blood corpuscles. It reaches a length of i-i-5 mm., 

 and secretes a delicate transparent tube, up and 

 down which it moves ; when feeding the oral end 

 of the ciliate may project from the tube. The red- 

 blood corpuscles are directed into the mouth by the 

 adoral zone of strong cilia fused into membranellas, 



NO. 2738, VOL. 109] 



pass into the protoplasm, and become enclosed in food- 

 vacuoles. The larger vacuoles may contain numerous 

 corpuscles which become compressed, and, owing to 

 the dissolution of the envelope of the corpuscles, the 

 haemoglobin-containing substance of all the red cells 

 in the vacuole merges into one homogeneous mass. 

 As digestion proceeds the vacuoles pass gradually 

 backwards, and pigment — agreeing in appearance with 

 melanin — is formed on the outside of the vacuole. 

 Haematophagus is unique among ciliates in producing 

 melanin as a result of the digestion of haemoglobin. 

 This pigment tends to accumulate in the hinder half 

 of the body, and the authors find evidence that when 

 the organism is full-grown the pigment is got rid of 

 by casting off that portion of the body prior to the 

 commencement of the resting, multiplicative phase. 

 How the blood of the whale becomes available to the 

 ciliate has not been established. 



Mr. C. H. Edmondson gives (Occasional Papers, 

 Museum of Polynesian Ethnology and Natural 

 History, Honolulu, 1920) a short account of the edible 

 mollusca of the Oregon coast. These are all bivalves ; 

 some, belonging to the genera Siliqua and Mya, are 



