144 



NATURE 



[August 3, 191 1 



canoes ol the rivals are each the dread sisiuL, which 

 has a horned snake's head at each end, and a two- 

 horned human head in the middle. Ii is an unlucky 

 mischance, in a volume otherwise so carefully pro- 

 duced, that four lines which should begin p. 4*51 are 

 printed at the top of p. 452, and it is only appreciation 

 of the great value !<>r reference of a series for which 

 we are heartily grateful to Dr. Boas and his university 

 that prompts us to beg that no future volume shall, 

 like this, be without an index. 



A. R. Wkic.11 1 . 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or 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 Nature of 7 Rays. 



Dr. E. von Schweidler pointed out in [905 thai an 

 effect (such as ionisation by a rays) due to a finite number 

 of independent events would be subject to fluctuations. 

 'the mathematical theory of the different experiments 

 which have been made to exhibit this with light, a and & 

 rays, has been developed by .Mr. N. R. Campbell. 



One of us began some preliminary experiments in 1908 

 at the Cavendish Laboratory to detect discontinuous effects 



with 7 rays. Two forms of apparatus have 1 n used in 



our experiments. In the first, two similar cylindrical 

 ionisation vessels were placed close together with their axes 

 directed to the source of the 7 rays — some radium. 



If the 7 rays have a spherical wave front, the two 

 similar vessels, being symmetrically placed with respeel to 

 the source, should be equally effected by the 7 rays, though 

 tin resulting ionisation due to the equal effects ma_\ not 

 be the same. If, on the other hand, the 7 rays are any 

 typ ol corpuscular radiation (in the Newtonian sense) 

 of a finite number of particles, the effect in the ionisa- 

 tion vessels would be unequal over short periods of 

 To compare the number of ions produced in the two 

 vessels, the electrodes were connected to an electrometer, 

 on,- vessel h,i n g positively, the other negatively, charged. 

 Ill- positive and negative currents from the two cans were 

 balanced as closeh as possible for long periods of time, 

 and so there was no large steady drift of the electrometer. 

 Mi. qn.ui/ fibre electrometer (Proc Camp. Phil. Soc, xv., 

 p. 106. 1909) showed fluctuations in the balance 



In the second apparatus a box-shaped ionisation can 

 with a central plane electrode was used. The positive ions 

 formed in one half of the can were received on one side 

 of die 11. ,i electrode, the negative ion, from the other half 

 of the can on the other side of the electrodi Large 

 fluctuations were observed when the source of 7 ' rays was 



!' ! I I" tile plaill- ..I the ele, Irode side ||,, | all I Ills 



experimental result would he explained it in the 7 ray 

 from radium ar.- projected particles, or (2) if the numbe 



mber 

 ravi 



ew of 



n pro- 



of ions produced in air In a constant source ol 



SubieCl I" fluctuations. 



We .-ne continuing the experiments with the 

 ! ivl it oat i eac h ..I these fac tot 3 plaj 

 'lie fluctuations observed. 



T. H. Laby. 



P. BuRBIDGE 



I he Ph\ sii al Laboi atorv, Victoria College 

 (University, N.Z.), Wellington, N.Z. 



The Occurrence of a Freshwater Medusa (Limnocnida) 



in Indian Streams. 



P \gharkar, lecturer on biology in the Elphin- 



College, Bombay, who has been kind enough to 



undertake the collection of fresh-water invertebrates on 



ol the Indian Museum, has recently senl me several 



■ is of a medusa from small streams in the Western 



I I Vlthough they were taken at so great a distance 



from the west cast ,,f India, it is important in note thai 



no. 2179, vol. 8;] 



these specimens were obtained from a river-system which 

 flows across the Indian Peninsula and reaches lie 

 than 500 miles awa\ on the shoos ol the Bay oi Bengal 

 Mr Agharkar writes as follows: — 



"The Medusa- were collected in deep pools ol the K 

 and Yenna rivers (tributaries of the Krishna), I was nol 

 able to get the hydroid form. I was told that the 

 M.-dusa- i.alled flowers or wheels by people) 00 

 larly in these rivers every dry season. Probably they are 

 present all the year round, only they are swepl away by 

 the currenl during the rain) season and a short time after 

 that. During the dry season, when the stream becomes 

 more or less a succession of deep pools, the) become very 

 marked. " 



In the- structure ol the manubrium and digestive system, 

 the position of the gonads, the structure "I the tentacles, 

 and the- form of the- umbrella these medusas agree pre- 

 cisely with Limnocnida tanganyicae. As regards generic 

 identity, there can, indeed, be no doubt, and there is 

 nothing in tie- spec im.-ns before me to suggest even a 

 specific difference. Tin 1 arc- nol. however, in a particu- 

 lar!) good si.ne of preservation, having suffered somewhat 

 in the post, and the question of specific identity may be 

 left unanswered until after an examination of fresh speci- 

 mens, which I anticipate no difficulty in obtaining al 

 suitable season. In the- meantime, I should Ice- extremely 

 grateful for well-preserved specimens of Limnocnida from 

 Africa in order that an actual comparison may be made 



N. Annaxdale. 



Indian Museum, Calcutta, July 7. 



Standard Time in Portuguese Territories. 



1 beg to inform you that Standard Time will be ii 

 from January 1, 1912, throughout Portuguese territoric 

 follows : — 



h. m. 



8 o E. Macao, Portuguese Timor. 



5 o K. Portuguese India (provisionally 5I1. 30m. E.). 



2 o E. Portuguese East Africa. 

 1 o E. Portuguese West Africa. 



o (Greenwich, or West Europe).- Portugal, St. 



Thome and Principe Islands. Whydah. 



1 o W. Madeira. Portuguese Guinea. 



2 o W. Ae.ores and Cape Verde I -lands. 



This observatory remains entrusted with the determina- 

 tion and the telegraphic transmission ol Standard Tim 

 the whole country, to the Lisbon time-hall, and to the 

 time station at the Meteorological Observatory, Ponta 

 Delgada (St. Miguel, Acores). 



I take this opportunity to state- also thai the most 

 trustworth) geographical latitude of this observatoi 

 lat. N. 38 4- 30-s" (prime vertical, meridian, and zenith 

 telescope series of observations from 1872 to the pre 

 printed or unprinted), and that the designation " Lisbon, 

 I apada, " is n,,w- the- most suitable- for 11, being similar, for 

 instance-. 1,, " |-'|, IM me , Arcetri," or "Naples, Capod - '- 

 monte. " 



For two years a new astronomical observatory ha- bi t 

 in existence and at work at Lourenco Marques; thi g -- 

 graphical coordinates are (transit pier): 



I n. S. 25° 58' 4')" +0-2" (meridian observation' ay 

 ( 'aptain t iago Coutinho). 



Long. I-. 32° 35' 39-4*±o-os" (moon culminations, Simula 

 taneously here, and geodetic connection with the 1 



Altitude- Hop ot pie 1 1. 59 metres. 



t dis.'i \ aieei io Astronomico de Lisboa, Tnpnda- 

 Lisboa-Portugal, July 25. 



Obsolete Botanical and Zoological Systems. 

 Wocii. some naturalist with a taste for bibliography be 

 sec goo.l as i,e mention books which contain tables di 

 obsolete botanical and zoological systems? Agassiz's 

 Essa) on Classification" and the article- on Zcol-egv in 

 th. "Encyclopaedia Britannica," ninth edition, furnish 

 use-ful examples, bul more are desire*! 



L. C. M. 



