55^ 



NATURE 



[January i6, igi; 



P/atmum sj3i 



The general character of the spectrum so secured 

 is solar in that it shows the F, G, H, and K Hnes, and 

 three broad absorption bands more refrangible than 

 K ; a bright line is suspected at 416/^^, but may be 

 merely a subjective phenomenon due to contrast. 

 Plates of other regions were taken, and agree in 

 indicating that the integrated spectrum of the Milky 

 Way is of the solar type. 



Dr. Fath suggests that his result differs from that 

 obtained at Harvard because he dealt with altogether 

 fainter stars, and that beyond a certain undetermined 

 magnitude stars of the solar type predominate. A 

 perfectly independent photographic investigation also 

 indicates that, in the mean, the fainter stars of the 

 Milky Way are the redder. These results, if they 

 prove to be perfectly general, are most important 

 from the cosmological point of view. {Astrophysical 

 Journal, vol. xxxvi., No. 5, p. 362.) 



Comets due to Return this Year. — Mr. HoUis, 

 continuing a function performed by the late Mr. W. T. 

 Lynn for many years, discusses briefly in The Ob- 

 servatory (No. 457) the periodic comets due to return 

 this year. Holmes's comet, period 6'S6 years, is due 

 to pass perihelion 

 early in the year, 

 but the conditions 

 are not very favour- 

 able ; it was ob- 



served in 1899 and 



1906. F i n lay ' s 

 comet, period about 

 6'5 years, was dis- 

 covered at the Cape 

 in 1886, and was 

 observed in 1893 

 and 1906 ; at the 

 latter return it 

 passed perihelion on 

 September 8. Both 

 these comets are of 

 the Jupiter family, 

 to which also be- 

 longs the object 

 (1906^') discovered 

 by Dr. Kopff in 

 1906, and calcu- 

 lated to have a 



period of 6'67 years. Two other comets may appear, 

 but are not expected with any great confidence. The 

 first, discovered by Mr. E. Swift in 1894, was con- 

 sidered to be possibly identical with de Vico's lost 

 comet, but has not been seen since, although a 

 thorough investigation gave a period of 6'4 years. 

 Finally, Westphal's comet of 1852, calculated to have 

 a period of about sixty years, may appear, and five 

 search-ephemerides for it have been published by Herr 

 Hnatek in the Astronomische Nachrichten, No. 4619. 

 Parallax Investigations. — In parts iii. and iv., 

 vol. ii., of the Transactions of the Astronomical Ob- 

 servatory of Yale University, Dr. F. L. Chase and 

 Mr. M. F. Smith publish the results of their helio- 

 meter observations of the parallaxes of forty-one 

 southern stars, most of wliich have large proper 

 motions. The methods employed and the individual 

 results are discussed at length, and then the final 

 results are collected into one table showing the mag- 

 nitude, spectrum class, position, proper motion, and 

 parallax of each object. Seven stars show a total 

 proper motion exceeding 1", and eight have parallaxes 

 exceeding o'l"; only two stars are common to both 

 categories. The volume concludes with a valuable 

 catalogue of the collected parallax results obtained at 

 the Yale Oliservatory for nearly 250 stars. 



NO. 2255, VOL. 90] 



EXPLOSIONS IN MINES.1- 

 A T the end of the report before us the Committee 

 -^^"^ gives the following short summary of its prin- 

 cipal contents : — 



"A method is described by which the relative in- 

 flammability of different dusts can be ascertained by 

 measuring the temperature of a platinum coil which 

 just ignites a uniform cloud of dust and air projected 

 across the coil fixed in a glass tube. It is shown that 

 the relative inflammability does not depend upon the 

 ' total volatile matter,' but on the relative ease with 

 which inflammable gases are evolved. 



"The order of inflammability so obtained corre- 

 sponds in a remarkable degree with the percentage 

 of inflammable matter extracted from the same coals 

 by pyridine. 



" We are of opinion that these two methods form 

 a valuable means of discriminating between different 

 coals in regard to the sensitiveness of their dusts to 

 ignition. It must, however, be borne in mind that 

 these tests have been made with dusts artificially 

 ground and sieved to an equal degree of fineness, and 

 since coals differ considerably in their power of resist- 



^-^>-r 



n" 



From an- blast 



Thcrmo-coupU 



-Apparatus for de 



Quartz cahd lory tube 



Thermo-couple lead 

 Heotinq current lead 



Enlarged section across c.d. 



ining the relative ignition-temperatures, ol coal-dust clouds. 



ance to pulverisation, the friability of a coal must be 

 taken into account." 



In the body of the report the subjects are discussed 

 under three heads : — On the relative inflammability 

 of coal dusts ; the effect of the admixture of an in- 

 combustible dust with coal dust ; and experiments on 

 the relative inflammability of different coal dusts at 

 Li^vin. Three appendices deal, respectively, with the 

 following subjects : — (i) The volatile constituents of 

 coal ; (2) the extraction of coal by pyridine ; (3) 

 analyses of coals and their relative ignition-tempera- 

 tures. 



From the results of the analyses contained in No. 1 

 appendix the Committee concludes that "all coals con- 

 tain at least two different types of compounds of 

 different degrees of ease of decomposition " ; that coal 

 " must be regarded as a conglomerate of which the 

 degradation products of celluloses form the base and 

 the changed resins and gums of the plants the 

 cement " ; that the latter are most readily decomposed 

 by heat, yielding as gases mainly the paraffin hydro- 

 carbons ; that these are probably the substances which 



> Second Report to the Secretary of State for the Home Department of 

 the Explosions in Mines Committee. Cd 643r. (London : Wyman & Sons, 

 Ltd., igta.) Price -jSd. The illustrations which accompany the present 

 article are from this report, and are reproduced with permission of the Con- 

 troller of H.M. Stationery Office. 



