272 



NATURE 



[June 5, 1919 



OVR ASTRONOMICAL COLUMN. 

 An Earth-effect on the Sun.— A shift of the lines 

 in the solar spectrum towards the red with reference 

 to the arc-lines which varies with distance from the 

 centre of the disc observed at the solar observatory at 

 Kodaikdnal has been attributed to an earth-effect, and 

 an attempt is being made to unravel the problem by 

 observing the spectrum of Venus at different phases. 

 The method of the scheme is to find if a similar shift 

 is apparent in the spectrum of Venus when illuminated 

 by the light of the solar hemisphere which is turned 

 90° or more from the earth, in which case the pheno- 

 menon of the shift of the lines, not being peculiar to 

 the part of the sun towards us, could not be ascribed 

 to a terrestrial cause. 



Dr. Gilbert Walker has suggested that the law of 

 increase of shift of the solar lines from the centre 

 of the disc to the limb as observed at Kodaikdnal 

 might be explained on the hypothesis of a constant 

 "relativity" shift towards red, combined with a shift 

 towards violet, due to a radial outflow of the gases 

 of the reversing layer. 



In his report of the observatory for the year 19 18 

 Mr. Evershed gives the recent progress of the in- 

 vestigation by saying that the Venus plates taken about 

 the western elongation of the planet when the angle 

 Venus — sun — earth was about 45° yield slightly smaller 

 values of the shifts, and there is a progressive diminu- 

 tion of wave-length as the angle at the sun increases. 

 When this angle exceeds 90° the displacements sun — 

 arc all have the minus sign — that is, the solar lines 

 reflected by Venus are shifted to violet instead of to 

 red with reference to the iron arc. Mr. Evershed 

 adds that the result of the Venus work seems to dis- 

 pose finally of the possibility that the solar line- 

 shifts are due to the gravitational effect resulting from 

 Einstein's generalised relativity hypothesis, and 

 thinks the facts undoubtedly show earth-effect, whether 

 the shift is interpreted as motion or otherwise. But 

 he thinks it is very desirable that confirmation of 

 these results should be obtained independently by 

 other observers. 



The Lunar Atmospheric Tide. — The object of a 

 paper read by Dr. S. Chapman before the Royal 

 Meteorological Society in February last, and published 

 in the April issue of the Quarterly Journal of that 

 Society, was to discuss certain recent determinations 

 of the lunar diurnal variation of barometric pressure 

 for Batavia and Hong Kong. Opportunity was taken 

 to refer to previous work and to review the present 

 state of knowledge of the subject. The lunar daily 

 barometric variation at Batavia has a semi-amplitude 

 of 0-065 mm. of mercury, which may be compared 

 with the semi-amplitude of 0-0090 mm. found by Dr. 

 Chapman last year from sixty- four years' observa- 

 tions at Greenwich. This lunar variation is purely 

 semi-diurnal, no appreciable diurnal component being 

 observable. It is independent of lunar phase, and 

 the data are inconclusive as regards the influence of 

 lunar distance; for, though the amplitude is probably 

 larger at perigee than . at apogee, the exact ratio is 

 not yet determined. The slight variation of ampli- 

 tude depending on the moon's declination which tidal 

 theory predicts is not detectable, but a marked 

 seasonal variation affecting both amplitude and phase 

 is rather surprising. The discussion of these results 

 for various stations shows that the amplitude 

 diminishes from the equator approximately as the 

 fourth power of the cosine of the latitude. These 

 departures from theorv in the value of this quantity, 

 which, it will be realised, is very small and difficult 

 of detection, lead to the conclusion that the lunar 

 atmospheric tide is not a simple tidal phenomenon, 

 but is complicated by other causes. 

 NO. 2588, VOL.. 103] 



THE DATE-PALM SUGAR INDUSTRY OF 

 INDIA. 



OUT of India's annual output of some 3,000,000 

 tons of crude sugar it is estimated that about 

 10 per cent, is derived from palms and about 4 per 

 cent, from the date-palm, cultivated for this purpose 

 in Bengal. Palm-sugar is obtained by making an 

 incision in the soft upper part of the stem, whereby 

 certain pathological changes appear to be induced, 

 which result in an outflow of liquid containing 

 sucrose. This liquid is collected and concentrated in 

 earthenware pots until it is of such a consistence as 

 to solidify on cooling, when it constitutes "gur" or 

 ''j^gg^fy.." a crude, dark brown sugar for which there 

 is a considerable demand in India. "Gur" is some- 

 times treated in native-owned refineries for the pro- 

 duction of a more or less white sugar by placing it in 

 baskets with pots underneath, into which the molasses 

 drains, the removal of the molasses being facilitated 

 by placing on the surface of the "gur" a layer, 4 in. 

 or 5 in. deep, of water-weed {VaUisneria spiralis) to 

 supply moisture. 



This process of producing palm-sugar has been 

 investigated recently by Mr. H. E. Annett, agricul- 

 tural chemist to the Government of Bengal,^ chiefly 

 with the object of placing the industry in a better 

 position to compete with sugar and molasses imported 

 from Java. 



In the second memoir Mr. Annett gives the results 

 of the investigations he has made with the view 

 of finding means of avoiding loss of sucrose, 

 ipiproving the quality of the crude sugar, modernising 

 rhe refining process, and economising in fuel. There 

 may be a considerable loss of sucrose by inversion 

 while the juice remains in the collecting pots. This 

 is reduced to some extent by the native process of 

 smoking the insides of the collecting pots before use, 

 but it can be further reduced by coating the insides 

 of the pots with lime-wash. By this use of lime the 

 yield of "gur" can probably be increased by about 

 20 per cent. 



The liquid as it exudes from the trees is normally 

 water-white, but rapidly darkens on boiling, due 

 mainly to the action of alkaline constituents of the 

 juice on the reducing sugars. This darkening can 

 be avoided by neutralising the juice with an acid 

 before boiling down. Suitable acid liquids are lime- 

 juice, alum solution, or aqueous extract of tamarind 

 fruits. 



A considerable item in the cost of producing palm- 

 sugar is fuel, which in some of the areas is scarce 

 and dear. Trials of an imported American maple- 

 sugar plant as a means of economising fuel gave dis- 

 appointing results, but it has been found possible to 

 make various suggestions regarding concentration 

 pans, the construction of the native furnace, and 

 possible waste combustible materials, the adoption of 

 which would lead to a reduction in the fuel costs. 



"Gur" made from juice collected in limed pots, 

 and carefullv concentrated after neutralisation with 

 acid, was of good colour, and gave the satisfactory 

 yield of 59 per cent, of refined sugar on treatment in 

 a centrifugal machine, whereas from " gur " made bv 

 the native process only 31 per cent, could be obtained. 

 A thorough trial of centrifugal machines for refining 

 the crude sugar in place of the tedious native process 

 is recommended. 



In his first memoir Mr. Annett made the useful 

 suggestion that it might be feasible to set un small 

 central factories for the production of refined palm- 

 sugar in suitable areas, supplies of juice being bought 



1 Memoirs of the Department of AKricnUnre :n Indi,i. Chemical Series 

 vol. ii., No 6, and vo'. v., No. 3. (Calcutta : Th.-icl<er, Spmk, and Co. 



