March 1, 1898.] 



KNOWLEDGE. 



61 



discrediting the catalogue, but in the hope that Prof. 

 Pickeriug may publish a supplement correcting any errors 

 in it that have since been detected, and making it complete 

 up to, say, magnitude G-5. According to his present views, 

 moreover, the kinds of spectra enumerated would, I believe, 

 be less numerous, E and 1 F practically disappearing. In 

 his late list of the spectra of bright southern stars in 

 the Aatrophi/xical .lournul the varieties of spectra are 

 indicated (when not exactly corresponding with a given 

 type) by the two types between which they lie, with 

 a figure indicating the position between them. Thus 

 ASF indicates a spectrum just halfway between A and F 

 (the estimate being made in tenths), while A 4 F indicates 

 that it is somewhat nearer to A than to F, and A 1 F is 

 very nearly equivalent to A. This kind of designation 

 will be found more convenient to those who are well 

 acquainted with the Draper Catalogue than the more 

 elaborate classification of Miss Maury. 



W. H. S. MoNCK. 



SPECTRUM OF o CETI. 



To the Eilitors of Knowledge. 



Sirs, — The reproduction of the spectrum of o Ceti is a 

 ninefold enlargement from a negative obtained on Novem- 

 ber 29th, on an Edwards isochromatic plate, with a small 

 direct compound prism near the focal plane of the fifteen- 

 inch objective. l\xtra breadth has been given to the 

 enlargement by a cylindrical lens. All the fine lines in the 

 picture have been verified by comparison with the negative, 

 which shows also many details lost in the enlargement. 

 Some of the lines and edges of bands are numbered for 

 reference to the following table of wave lengths : — 



which, by the kindness of the Eev. Espin, is in the 

 possession of the observatory ; but probably the lines S 

 and 7 are much brighter now, while ^ cannot be compared, 

 this region not being included in the copy of the Harvard 

 photograph. 



There appears to have been a progressive change during 

 the last seven weeks in the relative intensities of parts of 

 the continuous spectrum. The maximum brightness in 

 the accompanying photograph is between the numbers 

 three and four. On December 11th the brightest parts 

 are the two columns near No. 9, and on December 19th 

 this change is stiU more pronounced. 



Wax,ter Sidgreaves, S.J. 



Stonyhurst College Obsel•^'atory, 

 8th January, 1898. 



X Herculis and stars of this class, the minor differences 

 of which are under examination at present. 



The characteristic of the spectrum of o Ceti is its hydro- 

 gen radiation. The two brilliant lines Hj and H^ have 

 lost nothing during the last seven weeks. The missing 

 lines Hf and H^ would both be well marked on the plate 

 if their radiations arrived. Of the former there is no trace 

 on any of the plates. Of the latter there may be a feeble 

 representative : there is a weak division of the absorption 

 baud on the red side of No. 5, at the position of H^, 

 and this may be a remnant of H^ light unabsorbed by 

 the superposed origin of the dark band. 



Smaller photographs of the spectrum, by a half prism 

 and short focus camera lens, show the bright hydrogen 

 lines y, 5, 4, and'r^, with the dark calcium bands at H and K. 

 The hydrogen spectrum is therefore substantially the same 

 now as it appears on a copy of a Harvard College photo- 

 graph taken some time previous to the spring of 1892, 



ERRATA IX TIMES OF ECL1P8K3 OF THE MOON. 

 To the Editors of Knowledge. 



Sirs, — I expected you would have noticed in February 

 Number the erroneous times given for the moon's eclipse 

 in .January Number, but I do not observe any correction. 



Any great mistake in the XKutical Almanac is so unusual 

 that it is not wonderful it should appear in other publi- 

 cations ; but as all the eclipses of the moon for this year 

 are wrong in the Nuutical Almanar for 1898, it is of impor- 

 tance that it should be known. The errata are given in 

 Xiiutical Almanac for 1899, and the true values are given 

 in W'hitaln'i's Aliiianaclc, the nearest second ; but so many 

 almanacks have been more or less caught that you will 

 pardon me for sending you a line. Lewis Hensley. 



Hitchin Vicarage, 



February 22nd, 1898. 



' LIQUID FLUORIXE." 



To the Editors of Knowledge. 



Sirs, — In the article on "Fluorine" there is an ex- 

 _ ^ „ , , pression made use of which, I 



think, requires some explanation. 

 It is — " absolute zero, where, if 

 our present knowledge is of any 

 worth, the life of the universe itself 

 would be extinguished." 



What is the life here meant '? 

 Of course a much less minus 

 temperature than —210° would ex- 

 tinguish all animal life on any 

 planet ; the " life of the universe " 

 must be something else. 



3, Cator Road, ^- ^- ^«''^=^- 



Sydenham, S.E., 



2nd February, 1898. 



[In writing of a particle of matter, its energy of motion 

 — that is to say, its heat — may be considered as the vitality 

 of the particle. When we speak of " live steam," for 

 mstance, we mean steam at a high temperature and 

 pressure. Now, a gas expands by ^^lard of its volume (at 

 0' C. and 760 min. bar. pressure) for every degree 

 Centigrade through which the temperature is raised, and if 

 the temperature be lowered by one degree it contracts by 

 that amount ; so that " absolute zero " is the point where 

 the gas has contracted theoretically to nothing, namely, 

 — 273° C. At this point a gas has no volume and no 

 pressure, and may be considered as dead. This is what I 

 meant when I said that at absolute zero the life of the 

 universe itself would be extinguished. — C. F. Townsend.] 



-i^L J 



