20O 



NATURE 



[April 15, 1909 



ample density without it ; no clearing baths are necessary, 

 and the original developer works excellently for the second 

 ■treatment — in all these details the manipulation of the new 

 plate is simpler than what is desirable, if not necessary, 

 in the case of the autochrome. The colours of the omni- 

 rolore plate are much more transparent than those of the 

 autochrome, being applied as paints or varnishes instead 

 of being absorbed by translucent starch granules ; but this 

 method has its drawbacks as well as its advantages, for 

 the density of the colour is not even all over each little 

 patch of red and green. The colour is lighter towards the 

 niargins of the patches, and their shapes, too, are rather 

 "irregular, but doubtless improvements will be made in 

 these directions. The plates, as they are, are simple and 

 easy to manipulate, and give results that must be dis- 

 .tinctly useful to those who wish to reproduce, or, more 

 correctly, to imitate, by the simplest known method, the 

 colours of the objects they photograph. 



OUR ASTRONOMICAL COLUMN. 



Observations of Comet Morehouse. — Comet 1908c 

 was observed, with the 284 mm. Amici equatorial, at 

 Arcetri on forty-one days between September 4 and 

 December 7, 1908, and 127 determinations of its position 

 were made with the micrometer. These are now recorded 

 "by Prof. Abetti in No. 4316 of the Astronomische Nach- 

 richten, together with a valuable set of notes describing 

 the comet's visual appearance on a number of days. 



Mr. Metcalf's note and excellent photographs are also 

 reproduced, from the Harvard Circular No. 148, in the 

 •same journal. 



A series of six photographs taken at the Dominion 

 Observatory, Ottawa, between October 6 and November 26, 

 is reproduced and described by Mr. Motherwell in No. i, 

 vol. iii., of the Journal of the Royal Astronomical Society 

 (Canada). The comet was visible at Ottawa for more 

 than three months, but dense smoke and unusual cloudi- 

 ness prevented an extensive series of photographs from 

 heing obtained. Those reproduced show similar knots in, 

 and displacements of, the tail-matter, as previously re- 

 corded. On October 20 the head of the comet passed over 

 an eighth-magnitude star without perceptibly dimming it. 



Observations, of the comet, made with a sextant on 

 ■board the German steamship Paranagua, are recorded in 

 No. 4317 of the Astronomische Nachrichten. 



Measures of Double Stars. — The micrometer measures 

 of double stars made by Dr. Lau and Herr Luplau- 

 Janssen at the Copenhagen Observatory during 190S are 

 recorded in No. 4315 of the Astronomische Nachrichten. 

 The stars observed chiefly lie hetween declinations 0° and 

 20°, special attention having also been paid to neglected 

 pairs. In addition to the date, position-angle, and 

 distance, the authors give brief notes concerning the 

 colours of the components, and, where possible, compare 

 the values obtained with those computed from previously 

 published elements. 



Diameter and Position of Mercury. — In these columns 

 on December 24, 1908 (No. 2043, vol. Ixxix., p. 232), we 

 noted the corrections to the diameter and position of 

 Mercury, derived by Prof. Stroobant from the observa- 

 tions of the transit of the planet, on November 14, 1907, 

 made at thirty-three observatories. Since the publication 

 of the memoir in which he gave those corrections, Prof. 

 Stroobant has received observed values from eleven 

 additional observers, and has incorporated them in the 

 final results which appear in No. 4317 of the Astrono- 

 mische Nachrichten. 



These show, from the time between first and second 

 contact, that the planet's apparent diameter was 9"-i66, 

 whilst t_he_ observations of the third and fourth contacts 

 .?ive, similarly, 9"-092. These values correspond to 

 diameters, at unit distance, of 6"-20 and 6"-i5 respectively, 

 the latter being probably the more correct. 



The corrections to the equatorial and ecliptical co- 

 j?rdinates are found to be Ao = -|- 0-0705., A5=-o"-25, 



NO. 2059, VOL. 80] 



and A\ = -)-i"o3, A/3 = -)-o"-02, respectively, in the sense 

 observed-calculated. 



The agreement of the Italian observations of this 

 passage of Mercury with the data given in various 

 ephemerides is discussed by Signor Pio Emmanuelli in 

 No. no of the Revista di Fisica, Maiematica e Science 

 Naturali (Pavia) for February. 



The Vatican Observatory. — We learn from the Times 

 Milan correspondent that the inauguration of the new 

 section of the Vatican Observatory, which was to have 

 taken place on March 18, was postponed because one of 

 the components of the 40-cm. object-glass for the new 

 equatorial refractor was found to be defective, and has 

 to be re-cast. 



When this new section is complete the Gregorian 

 Specola will be abandoned, and the whole of the observa- 

 tory will be located on the summit of the Vatican hill, 

 100 metres above the square of St. Peter's, where Father 

 Lais has been engaged, since 189 1, in taking the photo- 

 graphs for the International Astrographic Chart (the 

 Times, Engineering Supplement, April 7). 



PRODUCER G.iS FOR ENGINES. 

 I. — Processes and Plants. 



TT is well known that what is technically called ' pro- 

 ducer gas " has been in use for many years in con- 

 nection with furnace work. Herr Bischof, of Magdesprung, 

 ivas the first to use an internally fired gas producer for 

 this purpose in 1S39; but little progress was made in our 

 country until 1857, when the late Sir William Siemens 

 introduced the combined gas producer and regenerative 

 furnace with which his name is associated. Some twenty 

 years later it occurred to me that a gas engine might be 

 worked with producer gas if a suitable plant were devised. 

 For furnace work the hot gas is taken direct from the pro- 

 ducer to the furnace without cooling or cleaning, and the 

 condensable hydrocarbon vapours, which usually accom- 

 pany the . gas, and add appreciably to , its value, are 

 burnt. But for engine work it is essential to wash and 

 clean the gas, especially as it must be free from tar. 

 It is also desirable that the gas should be cool when 

 it enters the cylinder of the engine. Incidentally, this 

 involves the removal by condensation, &c., of the con- 

 densable hydrocarbons which leave the producer, and after 

 their removal the gas must still be strong enough to fire 

 well and give good working' results in the engine. I 

 succeeded in making a suitable plant, and it was first tried 

 with a. small Otto engine in 1879; the results were good, 

 and they encouraged the makers of the engines to build 

 them of larger size so as to compete favourably with 

 steam-power. Many thousands of horse-power are now 

 working with gas plants of this type, and during the last 

 few years a still further impetus has been given to the 

 subject by the use of a modified plant, which is known 

 among engineers as a suction plant, and which will be 

 more fully described later. 



For the moment we will consider briefly the process of 

 making producer gas, and some of the chemical reactions 

 involved. Producer gas is made by forcing or drawing 

 air, with or without the addition of steam or water vapour, 

 through a deep bed of incandescent fuel in a closed pro- 

 ducer. Usually the fuel is fed in at the top, and the 

 currents of air, or of steam and air, enter at the bottom, the 

 gas outlet being near the top. An important characteristic 

 of the process is that no external heat is applied to the 

 producer, as in the case of an ordinary gas retort. When 

 once the burning of the fuel inside the producer has been 

 started, the air which is used to make the gas keeps up a 

 continuous process of combustion, and a sufficiently high 

 temperature is maintained to decompose the steam and to 

 effect other necessary reactions. 



We know that if there were a shallow fire of carbon- 

 aceous fuel and a sufficient supply of air, the carbon would 

 be completely oxidised. The product of this complete com- 

 bustion would bo carbon dioxide, with the development of 

 a large amount of sensible heat ; but if there were a con- 

 siderable depth of carbon in the producer (as there should 

 always be in practice) the resulting gas would be carbon 



