592 



NA TURE 



[April 19, 1906 



temperature of transition of sodium bromide dihydrate into 

 the anhydrous salt as a fixed point in accurate thermometry. 

 As the result of their investigations they conclude that 

 when the salt is quite pure the transition of the dihydrate 

 into the anhydrous salt lakes place at a temperature of 

 y, <. 7 _| c, but that the exact value of the transition 

 point is slighth modified b) the presence of ira.es ol 

 impurity. Considerable difficult) is experienced in pre- 

 paring pure sodium bromide free from sodium chl le ; il 



cannot be obtained by re-crystallising the ordinary bromide, 

 but must be made from pure bromine and pure sodium 

 carbonate Details are given of the methods used in puri- 

 fying these materials, the sodium bromide ultimately 

 obtained giving a value ol 23008 for the atomic weight of 

 sodium ; this valor agrees closely with that recently found 

 for the atomic weighl by the same investigators using a 

 method based on the analysis of sodium chloride. - 



The variation of the properties of the hydroxy! group 

 of alcohols as the nature and number of the alkyi radicals 

 attached to the carbon atom are varied forms the subjecl 

 ol a suggestive paper b; Prof. Louis Henry in No. 12 of 

 the Bulletin of the Royal Academy of Belgium. The 

 observations are of interest both from practical and classifi- 

 catory standpoints. Ii is pointed out that as the number 

 of alkyi groups is increased in passing from a priman to 

 a tertiary alcohol, the properties characterising the 

 hydroxy! pass from those associated with the hydroxyl 

 radical ol watei to those characteristic of the hydroxyl 

 such as potash. I n particular the different 

 behaviour is emphasised of the three classes of alcohols 

 towards the halogen hydrides, towards acetyl chloride, 

 and during esterification by means of hydrogen chloride 

 and a lain arid. The generalities established can be 

 utilised as a means of predicting the behaviour of the 

 mixed alkyi ethers when subjected to the decomposing 

 action of the halogen acids. 



A WELL-ILLUSTRATED priee-list of sundials and sundial 

 pedestals has jusl been issued by Messrs. Newton and Co. 

 Many forms of horizontal and vertical dials, and also 

 pocket dials, are described in the catalogue, which should 

 be seen b\ anyone who desires to possess a timekeeper ol 

 this kind as a reminder of the days when hours were 

 marked b\ shadows on a dial. 



A copy of the reporl for 1005 of the Rugby School 

 Natural History Society has been received. It is to be 

 regretted that " a distinct falling off in the keenness of 

 the sections taken as a whole" during 1005 was, accord- 

 ing to the preface, noticed b\ the officers of the society. 

 It may be hoped that the presenl year will, by iis ex- 

 ceptional exhibition of vigour, retrieve the character "I what 

 has been a hard-working society. 



lilt; Journal of the Royal Sanitary Institute (vol. xxvii., 

 Xo. ;,) contains the full text of the important series ol 



papers read al the conference en r k, abatement in 



December, 10115. The list includes the address by Sir 

 W. H. Preece, K.C.B., on factory ami trade smoke abate- 

 ment : and papers on stoking, by Commander W. F. 

 Cabcrne ; on the abatement ol smoke from factories, by 

 Dr. S. Rideal ; on the artificial production of persistent 

 fog, b\ the Hon. Roll,, R U ss || : on the destructive effect 

 of smoke in relation to plant life, by Mr. Arthur Rigg ; 

 on the work of the Hamburg Smoke Abatement Society, 

 bi Mr. J. B. C. Kershaw; on observations on smoke 

 densities, by Mr. J. \V. Lovibond ; and on the effect of 

 smoke on plant life, b\ Miss \l. Agar. 



MO. I9O3, VOL 71^ 



OUR ASTRONOMICAL COLUMN. 

 The Continuous Spectrum of the Chromospheri Vii 

 interesting communication dealing with the question ol the 

 existence of a continuous spectrum in the radiations 

 emitted b\ the chromosphere was communicated to the 

 Paris Academy of Sciences by M. Deslandres on March 26. 

 M. Deslandres made special preparations lor the eclipse 

 :n August last in order to determine whether the continuous 

 spectrum (i.e. the radiations emitted by solid or liquid 

 particles) of the chromosphere is brighter, as bright, or 

 less bright than that of the neighbouring corona. Employ- 

 ing coloured screens, which absorbed the gaseous radi- 

 .uii ris, In photographed the uneclipsed ring of chromo- 

 sphere and corona directly, and, in order to determine 

 whal proportion of the transmitted radiations was due to 

 the light emitted by the metallic prominences, \v., he 

 simulta uslv employed two grating cameras which dis- 

 closed the presence and intensity of the latter. 



Comparing the images photographed through screens 

 with similar ones obtained in the usual manner b\ Count 

 de la Baume Pluvinel, it was seen that the former ex- 

 hibited many striking peculiarities in the large group ol 

 prominences in the north-east quadrant. On lb'' si reen 

 photographs the prominences were much shorter than on 

 the ordinary photographs, whilst their base and a series 

 of nuclei towards the north were much brightei than the 

 oilier portions, features not noticeable on the ordinar) 

 negatives. Spectrograms of the c.ron.i secured at Palrria 

 b\ Dr. VV. J. S. Lockyer confirmed the results of Ibis 

 . c tmparison. 



M. Deslandres concludes that these prominences did emit- 

 .c continuous spectrum which was more intense than that 

 ol lb- neighbouring parts of the corona, and were far 

 richer in incandescent particles. A programme for the 

 prosecution of this important research in future eclipses 



op. ones M. Deslandres's communication (t'ciif 1 !'' 1 



rendus, Mo 1 j 1 



Objective-prism Determinations of Stellar Radial 

 Velocities.— Circular No. no of the Harvard College 

 Observatory contains a brief description ol some results 

 recenih obtained with the objective-prism method ol deter- 

 mining radial velocities. In this method an expi sure i 

 made in the usual way. then the prism is turned through 

 [80° and a similar exposure made, or the telescope may be 

 reversed and the photographic plate turned through 180 . 

 stars with known velocities serve .is standards lor the dis- 

 placement of the corresponding lines in the two spectra. 



\ reproduction of a spectrogram of the Pleiades, taken 

 on January 211 with the n-inch Draper telescope, is given 

 in the Circular. On this plate about a dozen stars could 

 be measured, and the probable error in the resulting 

 velocities would be about ±3-5 km. The scale is 

 ;,j"o o 1 cm., and the exposures were thirty-seven and 

 thirty minutes respectively. On another plate, secured on 

 January 29 with two exposures of about twenty minutes 

 each, about 100 stars could be measured, although a 

 number of them, owing to distortion at the edge ol the 

 plate, could only be employed to ascertain the corrections 

 necessary. 



In No. 2, vol. xxiii., of the Astrophysical Journal, Mr. 

 Geo. I'. Comstock discusses a similar method for deter- 

 mining radial velocities, but he proposes iwo similar direct- 

 vision prisms placed in front of the objective. Formulae 

 for calculating the velocities from the measures obi. lined 

 accompany Mr. Comstock's paper. 



Iiii. Observation of Loxo-period Variables. — In 



Circular No. 112 of the Harvard College Observi 'j Prof. 



Pickering publishes a plea for the organised observations 

 of long-period variable stars, observations which are 

 especially suitable for amateur observers. In ordei to 

 facilitate this work various catalogues of such -i.ir- have 

 alread) been published by the Harvard observers, and a 

 new inn, bringing the results up to date, is now in the 

 printer's hands. When published, copies of this catalogui 

 will be given to all observers who can make use ol il. 



A number of enlarged copies of Father Hagen's charts 

 of the fainter variables are also being prepared, and will 

 be supplied at cost, or given, to observers qualified to use 

 them. Instructions as to the improved method of making 

 these observations are included in the present Circular. 



