KNOWLEDGE & SCIENTIFIC NEWS. 



[November, 1906. 



ASTRONOMICAL. 



By Charles P. Butlek. A.R.C.Sc. (Loiid.>, F.R.P.S. 



Studies of the Sun's Heat Emission. 



MM. Cii. Fery and G. Millochau describe Ihoir prepara- 

 tions for making- a new series of determinations of tlic 

 sun's calorific emission, using for the purpose their pyro- 

 metric telescope. Thoy consider the apparatus specially 

 suitable for heat sources of definite area, as the recording 

 part may be adjusted with great delicacy. For these ex- 

 periments, a special form of the instrument has been con- 

 structed, consisting of a silvered-glass mirror, 103 mm. 

 diameter, and 800 mm. focal length. .At the focus of this 

 mirror is placed a thermo-electric couple of similar con- 

 struction to those employed in the Fery commercial p3'ro- 

 metric telescopes. Beliind the thermopile is a total reflec- 

 tion prism serving to direct the rays coming from the mirror 

 into an ocular, mounted on a movable dark hood. The 

 observer looks into this in a similar manner to that followed 

 when using a Newtonian reflector, and sees in the eye- 

 piece the thermopile, forming a reticule superpo.sed on the 

 magnified image of the celestial object under examination. 

 Delicate focussing mechanism is provided to adjust the 

 reticule exactly at the focus of the mirror. The telescope 

 tube proper is closed by a diaphragm composed of two 

 metallic rings, one fixed, the other movable. Each ring 

 has a sector opening of go", so that any required opening 

 may be used, the actual amount being recorded on a divided 

 circle. 



The current generated in the pile is measured with a 

 galvanometer having a movable coil. 



By permission of M. Janssen, it has been arranged to 

 make successive determinations at four stations of different 

 altitudes, Meudon (150 m.); Chamounix (1030 m.) ; (irand 

 Mulcts (3050 m.); Janssen Observatory, Mont Blanc 

 (4.S10 m.). 



The obsiTvalions will be of two classes : — (i) Measures 

 taken at various hours of the day, by placing the centre of 

 the sun on the centre of the thermo-electric reticule. (2) Ob- 

 servations of the various amounts of radiation of the several 

 parts of the solar disc. This will be done by allowing the 

 solar image to drift over the reticule, noting the galvano- 

 meter readings and the times ; then by plotting the readings 

 the values for any section can be deduced. 



It is stated that the curves obtained thus far agree with 

 those shown by \^■ilson's 1S94 results. — {('ntnptrs licndus, 

 M.v !'■ 5"5. October, 1906.) 



Recent Views on Terrestrial Magnetism. 



M. Carl .Stiirmer has for some time past been developing 

 a mathematical theory of the aurora and magnetic perturba- 

 tions in relation to Birkeland's hypothesis, supposing that 

 these effects are due to electric corpuscles emanating from 

 the sun, and moving under the influence of terrestrial 

 magnetism. He gives certain of the formula derived bv 

 Poincare's method, showing that it may be possible for a 

 swarm of electric particles moving along certain trajectories 

 to show evidence of perturbations more or less periodic. 

 The velocities used in the discussion are tho.se given by 

 Rutherford for cathode rays, and the a and (3 rays of radium. 

 'J he values determined arc found to be of the same order 

 as Eschenhagen's oscillations, and the dimensions of the 

 trajectories vary greatly with the n.-iture of the corpuscles. — 

 (Cumptes Hciiilus, 143, p. 460, October i, igo6.) 



Colours and Spectra of Solar 

 Prominences. 



M. Ricco, observing at Alcala de Chisvert, in Sjjain, 

 duiing the last total solar eclip.se, on August 30, 1905, ob- 

 tained direct photographic confirmation of the continuous 

 spectrum of the solar prominences, which has been 

 described by M. Deslandres. As seen visually, the 

 prominences were of different colours in different parts; the 

 bodies of the prominences were purplish red ; the circumfer- 

 ence of the chromosphere was purplish ; and the summits 

 of the jets were very clear purple, almost white, and very 

 biilliant. Several chromos])heric plumes were seen suffi- 

 ciently colourless to correspond with the white prominences 

 recorded by Tacchini. 



Of especial interest are the results found on the photo- 

 graphs taken with a prismatic camera, showing mono- 

 chromatic imajjes of the uneclipsed parts of the solar sur- 

 roundings. These show many important variations in the 

 radiations of hj'drogen, helium, and calcium. The photo- 

 graphic Ullages of certain prominences in K light show a 

 height of 79 "-83" while the same objects seen visually 

 in the C line were only 64" high. It is suggested that 

 this greater height of violet radiation may be the cause of 

 the phenomenon of white prominences. Several of the 

 prominences show definite continuous spectrum from the red 

 to ultra-violet ( X 3600). There appears to be a special class 

 of prominence formed solely of calcium vapour. 



Total Solar Eclipse of August 30, 1905. 



Spectra vf Chromosphere and Corona. — Professor F. W. 

 Dyson has made a complete examination of the spectra 

 photographed by him with the slit spectroscope, and in- 

 cluded in the discussion the results obtained with the same 

 instrument during the previous eclipses of igoo and igoi. 

 Observing in 1905, at Sfax, he was able to secure an ex- 

 cellent photograph of the corona spectrum, showing several 

 new lines. The list of chromospheric lines given from the 

 combined photographs is very complete, extending from 

 X 3347.98 to A 5875.87, and shows the intensity, probable 

 orijj;in, laboratory intensity in spark or arc, and details by 

 other workers for each line. Detailed discussion is given 

 of the mode of occurrence of each element. It is noticeable 

 that the helium lines and the element giving X 4685. 86, are 

 stronger in the higher than in the lower chromosphere. 

 The enhanced iron lines appear to be weakened in the 

 higher chromosphere in comparison with the magnesium 

 arc lines and the enhanced titanium lines. From the ex- 

 perience gained in the.se three eclipses, the author concludes 

 that a slit spectroscope is most advantageously used when 

 it is adjusted as nearly as possible tangential to the sun's 

 limb at the point of second' contact, this applying both to 

 the chromospheric and the corona spectrum. The paper is 

 illustrated by an excellent reproduction of the corona 

 spectrum, showing the two new lines at 5117 and 5563. — 

 (Phil. Trans. Boyal Society, Vol. 206, Series .\, pp. 403-452.) 



I'hoUxjraphs of Corona. — The Rev. A. L. Cortie 

 took charge of the Stonyhurst College Expedition 

 to Viniiroz, Spain. His chief instrument was the 

 coelostat and long-focus lens belonging to the Royal 

 Irish Academy, which had been used in 1900. Six 

 Ijhotographs of the corona were obtained, the size of the 

 moon's diameter being about 2J inches, the exposures 

 varying from 4 to 50 seconds. After the very striking 

 prominences in the north-east, the most conspicuous object 

 is a group of plumes with a decided dark ray about position 

 angle + 1250.2. The dark ray can be traced to about 12' 

 from the moon's limb, and both its darkness and its peculiar 

 character dilTerentiate it from the other rifts between 

 streamers. As it rises it curves somewhat towards the 

 north, and l:)ecomes broader. In negative 4, another 

 dark ray seems to be superposed on the bright plume at 

 posilion'angle + 136'', but this cannot be traced on any other 

 photograph. The paper is illustrated bv four reproductions 

 of the corona.— (frans. Hoy. Irish Academy, xxxiii.. Sect. 

 A. Part I.) 



