526 



NATURE 



rr 



1912 



r even the decliii.iiiuii instrument flave tnuili!.- ni 

 ika{:jc of steam pnst piston valves ! 



n ri -;'':irrh ciuHluitrd nt HifiniiiL;' 

 V Mi nzil I.i>!>lr'\, .111(1 111.- rr-;nlts , 

 arti' \'.)\yjiu-i'r fi.r l'"i'l>i-ii.ii-\ .i. A 



cyliii' • ■ ' • us'-il, :\\''\ I iiiiM !.,. iijii'''' 

 saturated steam 01 o 900° \' . 



The valve could b( < ^ means of 



an electromotor. The principal conclusions 

 follows : — (a) Piston-valve leakage is not rnspc; 

 any appreciable amount of the " missing quantii 

 leakage of a well-fitted piston valve is practic iHv 

 (6) The leakage does not follow the 1: 

 (c) The leakage diminishes proportionally to .;,, ,,,._...,, 

 of temperature until 500° F. is reached, after which the 

 distortion of the rings causes it to increase. From these 

 results it appears that the piston valve has advantages 

 over the flat slide valve other than those due to the 

 fact that the piston form is balanced. It is probable, and 

 indeed is almost proved by Callendar and Nicholson's 

 experiments, that the great difference in leakage of the two 

 types is owing to the fact that slide valves warp, and thus 

 lift off the face. Warping is eliminated in piston valves, 

 except at high temperatures, and hence the leakage is very 

 small. 



Mr. Frank Fielden deals with a few problems in 

 bituminous suction-gas plants in Engineering for 

 February 9. An examination of the specifications issued 

 by suction-gas plant makers shows that in most cases a 

 good average quality of dry anthracite coal of a certain 

 size is expected to be used to fulfil the guarantees as to 

 fuel consumption and quality of gas to be produced. 

 There are, however, strong incentives to the engineer to 

 <;onstruct a suitable suction-gas generator for the satis- 

 factory gasification of native coals, which have hitherto 

 been unemployable for the purpose. Mr. Fielder sum- 

 marises the ideal suction plant as follows : — It will con- 

 sume all the volatile matter contained in the coal in 

 addition to the solid carbon ; to effect this, some mechanical 

 feeding of the fuel at a regular rate to suit the load on 

 the engine would seem desirable. Caking coal will be so 

 treated as to prevent arching over, and consequent obstruc- 

 tion to an equable air and vapour supply in the main fuel 

 column of the generator. Suitable facilities will be pro- 

 vided for the effectual removal of ash and clinker without 

 interfering with the quality of gas produced ; this is 

 ■essential for all coal used on extended periods of running. 

 It is, of course, assumed that the ordinary factors will also 

 be considered, such as amount of space occupied, simplicity 

 of construction, minimum amount of attention, and reason- 

 able first cost. 



OUR ASTRONOMICAL COLUMN. 



The Changes on Saturn's Rings. — From the current 

 number of The Observatory we learn that Prof. Todd 

 claims an alternative translation for his telegram (which 

 was in Latin) concerning the changes on, and probable 

 " dissipation " of, Saturn's rings. It is suggested that the 

 term " dissipation " did not refer to the actual rings. 



Ephemeris for Borrelly's Comet, 191 le. — In No. 4552 

 of the Astronomische Nachricltten M. Fayet gives a bi-daily 

 ephemeris for comet 191 le extending to Mav 13. The 

 comet is at present in Perseus (R.A.=3h. 54-8m., 

 5 = -+-45° 57'), and is travelling towards Auriga in a direc- 

 tion slightly north of east; it is, however, very faint, and 

 is receding from both the earth and the sun. 



NO. 2207, VOL. 88] 



Stki.i.ak Si-ixm Ukgio.s.— Although the 



i)hut(jL'rai)liic sp'-i I ivr Ijeen more or less 



studi'd in the rej; refrangible than 



,dy of the less rtfi region has been 



d, except for a few of the brighter stars, by the 



sensitiveness of photographic plates in that region. 



.\n nicmpt to remedy the omission apprnrs in No. 4552 



I if t})<- Astronomische Nachrichten, v.h<r'- Dr. Hnatek 



(HlljlisiliJS rrdlictioim <<{ tin >^i)f(lr;i (,f v Andromcdae, 



a Cassiopeia us less 



rf^fr.nnfjihlo t^ ; 1907, 



ndorff 

 ; pina- 

 cyaiicii-iiaiiii-a piat'-s, uy w rau.-n and w ainwriglit, were 

 employed, but the spectra are still under-exposed. 



11,,. ,-,,r|ii,-t;,>nt are not v'"> ■■■'■hnustive ; for example, 

 nine lin spectrum of a Cygni 



I and A whereas the South 



Kensington published reduction gives twenty-eight. 

 Further, he gives, generally, Rowland's origins and in- 

 tensities, which in an " enhanced-line " star do not repre- 

 sent the facts ; only occasionally does he refer to the 

 enhanced lines published by Lockyer, and thus at times 

 misinterprets the significance of an origin, or an excep- 

 tional intensity, of a line. For each star he has deduced 

 from his measures the radial velocities at certain epochs, 

 which he tabulates at the end of the paper. 



Stellar Parallaxes. — .\ second series of stellar 

 parallaxes, determined from meridian transits at the 

 Washburn Observatory, Wisconsin, is published by Mr. 

 A. S. Flint in No. 631 of The Astronomical Journal. The 

 observing list consisted primarily of stars between magni- 

 tudes 1-5 and 2-5, but some fainter stars were added, and 

 in the final list are given the parallaxes of 124 stars. 

 Among the brighter stars the following large positive 

 parallaxes are given : — )3 Persei, -t-oi3o' ; o Persei, 

 -I-0109''; /3 Canis Maj., -t-0163'' ; a Geminorum (pair), 

 -I-0-I74''; y Leonis, -ho-ios" ; /3 Ursae Maj., -^0136'; 

 a Serpentis, +o-i5i'' ; and a Ophiuchi, -(-o-i27'; while the 

 3-7-magnitude star c Eridani has a parallax of -f-o-379' in 

 Mr. Flint's list. A general average of the probable errors 

 of the final parallaxes is ±0031", and after discussing the 

 data in a number of different ways Mr. Flint concludes 

 that the parallaxes given are sensibly free from systematic 

 error. 



The Spectra of Comets. — The February number of 

 L'Astronomic contains an interesting paper in which 

 Comte A. de la Baume Pluvinel discusses the spectra of 

 comets, more especially as revealed by the researches of 

 the past few years. 



After briefly summarising the earlier observations, he 

 describes at length the spectrum of the Morehouse comet, 

 and reproduces an excellent comparison showing the close 

 identity of the doublets in that spectrum with doublets 

 occurring in Prof. Fowler's spectrum of carbon monoxide 

 at low pressure. 



In conclusion, he points out that to answer the ques- 

 tion, " What are comets made of? " would have been com- 

 paratively simple, say, a dozen years ago, but to-day the 

 photographic method has revealed so much that was then 

 unknown that the answer is not so easy. The composition 

 of comets is complex, and all comets do not display the 

 same composition. As our knowledge extends still further 

 it may become necessary to classify comets in spectral 

 classes ; in fact, this has already been done in a simple 

 fashion. Some comets are essentially gaseous and blue, 

 e.g. Morehouse : others, like the great comet 1910a, are 

 yellow, and contain much solid matter. 



The Parallax and PRorFR Motion of Mira.— In No. 

 44 of the Mittcilungrn drr Xikolai-Hatipistermcarte cm 

 Pulkowa Herr S. Kostinsky discusses at length the 

 parallax observations of Mira made by him during the 

 period 1903-7. The main discussion is printed in Russian, 

 but there is a risumi in German, in which the principal 

 stages and results are described. 



Among other results, the author finds that the yearly 

 parallax of Mira is probably zero, and in any case does 

 not exceed -i-oos". The vearlv proper motion in R.A. is 

 extremely small, and in declination is about -o-2-,;*. 



