November, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



275 





ASTR.ONOMICAL. 



By Charles P. Butler, A.R.C Sc. (Loud ), F.R.P.S. 

 Variation of the Figure of the Sun. 



In the early seventies Lewis M. Kutherfurd obtained a con- 

 siderable number of excellent photographs of the sun at his 

 private observatory, and these were later presented by him to 

 the Observatory of Columbia University, New York. As it 

 has been shown that stellar photographs taken by the same 

 astronomer are capable of giving results comparable with the 

 best heliometer determinations, Prof. C. L. Poor, of this 

 Observatory, has lately been induced to examine the old 

 solar photographs with the oliject of finding any evidence of 

 changes in the form of the solar disc. 



In all there are ijij photographs, extending over the period 

 1S60-1S74, but part of these were only with a small lens. 

 Those taken from 1868-1874 were with his 13-inch telescope, 

 and of these plates 22 have been selected as suitable for 

 minute measurement, and on each the polar co-ordinates of 

 twenty-eight points round the limb have been determined. 

 Dividing these into two sets and taking means, it was possible 

 to obtain a most probable value for the polar radius, and for 

 the equatorial radius, of_ the solar disc on each plate. The 

 differences of these radii are tabulated in order of time, and it 

 is shown that there is a consistent agreement for the plates of 

 any one year, but that the plates of different years differ 

 radically. Thus the plates in 1S71 show the equatorial radius 

 to exceed the polar by some o"-^, while the plates of 1870 and 

 1S72, on the other hand, show the polar radius to be the greater 

 by about o"'2. A critical examination of the records shows that 

 the instrumental conditions, time of exposure, orientation, &c., 

 were as nearly as possible constant, and it must therefore be 

 due to a real expansion and contraction of the sun's disc. 



An interesting confirmation of these conclusions was then 

 furnished by a discussion of the heliometric measures of the 

 sun's diameter which were made by the German observers in 

 preparation for the transits of Venus in 1874 and 18S2. Pro- 

 fessor Poor has arranged all these solely with respect to time 

 of observation, and finds they readily fall into two series, one 

 from September, 1873-January, 1875, the other from May, 

 1880-June, 1883. In both of these groups it was found that 

 there was a progressive change, and that of the first group wa=; 

 in the same direction as that indicated by the Rutherfurd 

 plates, while the second group was opposite. Thus during the 

 interval from 1S81-18S3 the equatorial diimeter was apparently 

 growing longer in relation to the polar diameter, while during 

 the former period, 1S74-1875, the equatorial diameter was grow- 

 ing relatively shorter. 



Again, photographs of the sun taken at Northfield, Minne- 

 sota, by H. C. Wilson, during 1893-181)4, indicatea shrinking of 

 the equatorial diameter with respect to the polar diameter. 



On examining the epochs of these changes, it is at once 

 apparent that they have a distinct relationship to the curve of 

 sun-spot frequency, and on plotting the values there is good 

 agreement as far as the observations go. 



These investigations seem to show, therefore, that the ratio 

 between the polar and equatorial radii of the sun is variable, 

 and that the period of this variability is the same as the sun- 

 spot period. The sun appears to be a vibrating body whose 

 equatorial diameter, on the average, exceeds the polar 

 diameter. At times, however, the polar diameter becomes 

 equal to and even greater than the equatorial — the sun thus 

 passing from an oblate to a prolate spheroid. It is possible 

 that in this variable figure of the sun may lie the explanation 

 of the anomalies in the motions of the planets Mercury, Venus, 

 and Mars. 



Pola-risation Observations during the 

 Solar Eclipse, August 30th, 1905. 



A \ ery interesting series of polariscopic determinations are 

 reported by M. Salet, who was appointed by the Paris Bureau 

 des Longitudes to observe the recent total solar eclipse at 

 Robertville in Algeria. 



His first effort was the endeavour to detect any existence of 

 a magnetic field in the neighbourhood of the sun bv observing 

 if the plane of polarisation of the coronal light suffered any 

 deviation. This plane should, from reasons of symmetry, be 

 radial if no magnetic field existed in the gaseous atmosphere. 

 For these observations an equatorial telescope of 95 mm. aper- 

 ture was employed, furnished with cross wires and a Savart 

 polariscope placed before the eyepiece. This can be turned, 

 before the observation, so as to suppress the bands due to 

 terrestrial polarisation. During totality the bands were well 

 seen on the corona. The plane was found to be deviated in 

 the right hand direction by 2° S. The smallness of this indi- 

 cates that the sun has, in spite of its mass, only a slightly 

 magnetic field. 



With another apparatus M. Salet was able to obtain good 

 photographs also of the coronal polarisation, showing fifteen 

 bands on the width of the solar diameter. They are visible 

 for about a diameter and a half from the solar liml), practically 

 up to the edge of the external corona. The polarisation had 

 a maximum intensity about 5' or 6' from the sun's limb, the 

 plane of polarisation being ahuost radial, and the slight devia- 

 tion measured visually was thus verified. A promuience 

 found crossing two bands apparently suffered no change of 

 intensity, showing without doubt the non-polarisation of the 

 prominence light. On none of the plates is there any trace of 

 atmospheric polarisation outside the corona or on the moon. 



For comparison, several observations were made of atmo- 

 spheric polarisation by means of two Savart's directed go" 

 from the sun, but at this distance no bands were visible during 

 totality. At 30^ or 40° from the sun, however, the bands were 

 easily scan during totality. In the neighbourhood of the sun 

 the plane of polarisation was vertical. 



A spectroscope was also provided with half its slit covered 

 by a nicol. The spectra obtained show different intensities on 

 the two halves by reason that on one the reflected solar light 

 is suppressed by the nicol. The coronal radiation, strong up 

 to 4 from the limb, is shown on both sides. Rays of hydrogen 

 and calcium are also shown, and others which will be measured 

 later. 



CHEMICAL. 



By C. AiNswoRTH Mitchell, B.A. (Oxon.), F.I.C. 



The Chestnut Flour of Corsica. 



The chestnut is the wheat of Corsica, and its flour is used 

 in the form of bread or polenta by the peasants throughout 

 the island. The chestnuts are slowly dried over a small wood 

 fire and stored until required for grinding. The mills are of 

 the simplest construction and consist of a wooden water 

 wheel whose axis turns a millstone which crushes the shelled 

 chestnuts against a fixed stone. The cheaper grades of flour 

 are of a dirty colour owing to the presence of particles of the 

 shells, and contain between II and 12 per cent, of moisture. 

 The composition of different varieties of the flour has been 

 determined recently by M. Comte, who finds that chestnut 

 flour closely approximates wheat flour in its food value. It 

 contains about the same amount of starch, more fat and cellu- 

 lose, but less nitrogenous substances (7 to 9 per cent., as 

 against 12 to 16 per cent, in wheat flour). Chestnut flour 

 attracts moisture very rapidly, and therefore soon becomes 

 mouldy unless kept in air-tight vessels. It has also the draw- 

 back of being very refractory to the action of yeast, and thus 

 producing an inferior kind of bread. 



The Formation of Ozone by Ultra- Violet 

 Light. 



It has been shown that the ultra-violet light emitted by an 

 electric mercury lamp produces violet colorations in glass 

 containing manganese which are otherwise only produced 

 very gradually by sunlight under normal conditions (" Know- 

 ledge AND Scientific News," this Vol., p. 158). The ultra- 



