NATURE 



[ February 13, tgig 



: is I RONOMICAL COLl \l \ 



I ni. PULSATION I in 1 ; 1 PHE1D \ u;i \i .11 1 1 1 



The Monthl) Notices for November lasl contain a 



; .ni this subjecl b\ Prof. Eddington, who selects 



een C'epheids, thi light-curves of which are well 



n, to 1. si thi theor y. Mi. absoluti magnitudi 



1 ii ni thi pei iods, using .1 diagi am gi\ en b; 



Mi Shapl y, arid the effectivi lemperatures and densitii 



1 r paper of his own. Prof. Eddington finds 

 thai all tb. stars are in a gaseous state throughout 

 their \.>lum. . xo pt the two ol 1 olute magni- 

 tude ; h meets this with the fad that Mr. Shaplej 's 



diagram shows a linear relation between period and 

 magnitude for the brighti r stars, but a curve for the 

 Fafntei ones, ["hi radius of Y Ophiuchi, the brightest 

 -in on the list (abs. mag. 4), is given as 

 42,000,000 km., 1I1. mas being thirteen times the 

 sun's; on thi average, the semi-amplitude <>f the 

 pulsation is 1 13 ol thi radius. Assuming an 

 tive tempei un nal ■ thi Foui th root of the 



luminosity, thi semi-amplitude ..I the temperature 

 fluctuation i 1/12 of the whole. Prof. Eddington 

 also deduces thai with period y$ days should corre- 



sp I pei ral typi FSJ, and with period 30-8 days 



type 1.,'. These deductions are in fair accordance 

 with Mr. Shapley's latesl observational results. 



Prof. Eddington directs attention to an erratum in 

 his former p. qui- on the radiative equilibrium of the 

 stars, the radiation pressure being taken ai four times 

 its true value. The error may be corrected bv multi- 

 plying the adopted molecular weigh! by 2S. It will, 

 however, make the calculated duration of the Giant 

 stage even shorter than before. 



Calcium Clouds in hf Milki Way. — The February 

 Observatory contains a letter on this subject 1>\ Mr. J. 

 Evershed. The suggestion was first made in thi casi 

 ..1 8 Orionis that it was surrounded In such clouds, 

 siiicr the H and K lines did nol share in the orbital 

 motion. Mr. Evershed now shows that the same is 

 the ease in Nova Aquilae, Nova Persei; and Nova 

 Geminorum (2), and quotes five other stars in Aquila, 

 Scorpio, Perseus, and Orion showing. the same pheno- 

 menon. In all cases the radial motion indicated by the 

 H, K lines agrees within some 4 km. /sec. with that din- 

 to the sun 's motion (assumed 20 km. see., towards t8h., 

 + 30 ). Hence the .allium clouds would appear to 

 lie practically at rest with respect to the star system, 

 the attraction of the stars upon them being, perhaps, 

 nearK balanced b\ radiation pressure. It will be 

 remembered that the Orion nebula also appears to 

 have no line-of-sight velocity other than that due to the 

 s. ilar iii.ui. hi 



Mr. Evershed notes that the phenomenon i- rendered 

 easiet of detection in novae owing to the large dis- 

 11! of tin II line in the star's own spectrum, 

 which separates it from thai due to the cosmic cloud. 

 The latter is seen as a fine absorption line on the 

 In.... hydrogen band II. "I the nova's spectrum. 



A •• New Navigation" Method. In " Notes on the 

 Working ol 'New Navigation'" (Cairo: Govern- 



ment Press, . Dr. John Ball gives a convenient 



method of calculating altitude from hour-angle (h), 

 latitude 1/), and <i 1 ation (d). First find an auxilian 



angle M from tin 



Then 



., /.I). 



equal ion 



M ■ cos / cos d. 



in(M + ^) S in(M-^). 



I s. upper sign for /. ./ same name.lowei fot contrary 

 nam.'. Dr. Ball points .mi the advantages ol the mi 

 both for navigation and land-surveving. He might, 

 however, have alluded in the very' useful Altitude 

 rabies" ..1 his namesake, thi Rev. F. Ball, R.N. 

 (London : J. I). Potter), which give the altitude, with- 

 out calculation, foi even degree ..l I, ,/, h to an 

 ac> ..1 .. 1 ' 1 .1. a. h 1. 



/ III-. WORK OF Till- GO\ ERA WENT 

 I IBOR 17 1 'AM . 



L?KO.\l thi recently issued annual report ..1 thi 

 - 1 Government Chemist on the work of the Govern- 

 ment Laboratorj (Cd. 9205), it appears thai the total 

 number of samples examined during the rear 1917-18 

 was ■■..0,453. 



Work for several new departments, including tin- 

 Air Board, the Ministry ol Food, and the Coal Con- 

 troller's establishment, was undertaken during the 

 year. Tin- aggregate number of samples analysed, 

 however, was some 58,000 less than in the preceding 

 twelve months. This decrease is attributed chief!} 

 to a fallin^-olf in the work required for the Customs 

 and Excise Department. Following upon diminished 

 imports, fewer samples of imported goods wen- taken 

 foi analysis; and war-time restrictions affecting the 

 home consumption of wines and spirits similarly 

 caused a reduction in the amount of analytical work 

 required. 



On the other hand, much of the laboratory activity 

 has been devoted to matters arising directly out of war 

 conditions. Among points of special interest maj bi 

 noted thi analytical control over the quality of food- 

 stuffs and medical supplies for the lighting forces, and 

 over the composition of metals employed in naval and 

 aerial constructional work. 



More than 20,000 samples of foodstuffs were 

 examined in connection with the feeding of the 

 Expeditionary Forces. This work was carried out 

 partly at the chief laboratory, and partly In officers 

 of the laboratory stationed at the various supply bases. 

 The quality of the supplies was controlled "by first 

 examining samples tendered by contractors, in order 

 to ascertain whether the conditions of the specifica- 

 tions were complied with. Specimens of the foods. 

 actualh, delivered were afterwards analysed, to ensure- 

 that the deliveries compared satisfactorily with the 

 selected " tender" samples. Most of the analyses wen 

 made on specimens taken from contractors' deliveries 

 in course of transit to the Forces, the goods being 

 detained until the report upon their quality had been 

 received l>\ the Army authorities. A salutary check 

 was thus in operation against any tendency to unlaii 

 dealing. 



The scientific public, and also thi general public, 

 would no doubt be interested in knowing whether any 

 adulterations or other attempted impositions were dis- 

 covered, but on this point the report of the Govern- 

 ment Chemist is silent. Still, it may safely be 

 assumed that the systematii examination of supplies 

 would in am case be a strong deterrent against 

 attempts to substitute inferior articles. It may be 

 taken foi granted, therefore, thai tin laboratory con- 

 trol has both conduced to the efficiency of the fighting 



forces and effected economy of public moivw . 



For the Army Medical Department 960 samples ..1 

 medicinal articles wen- examined. A^ might be ex- 

 pected, these consisted largely of anaesthetics. It is 

 scarcely necessan to point oul thai the comfort, and 

 often tin life, of wounded soldiers under anaesthesia 



NO. 2~,J2. VOL. I02 



