1901.] 



KNOWLEDGE. 



133 



J. A. Allen nieutions that tbo first susiirestiou of tho dis- 

 tiuL'tnoss of thoOreonlaiul from tho Anioriiiui form ajipeariHl 

 in Knowledlie. iu the artiole on the vouii'; musk-ox at 

 \Vol>uni. It is true that the autliorof that article, misled 

 l\v some badly-executed photojirajihic reproduetious, did 

 not at that time realize the eoustaney of the distinctive 

 features he I'ointed out as dift'erentiatint; youn^' Greenland 

 musk-ox from the American representative of the sjiecies. 

 But iu his subsequent separation of the Greenland form, 

 on account of its white face-markings, as a local race he 

 has been fully justified by the American material. Indeed, 

 on account of certain differences in the form of the horns 

 and hoofs. Dr. Allen would go one step further, and con- 

 sider the Greenland musk-ox entitled to rank as a separate 

 species, under the name of Ovihog trarJt. 



In the Ajiril issue of the Procefidiiujs of the Zoological 

 Society of London are published extracts from a letter 

 addressed to the Secretary by Sir Harry Johnston, relative 

 to a hitherto unknown mammal of the aiiproxiniate size 

 of a horse inhabiting the Aruwimi, or Congo, Forest iu the 

 country between Lakes Albert and Alliert Edward. The 

 animal, which is known to the natives as the okapi, was 

 described to Sir Harry as being iron-grey, or dun, above, 

 with the legs and uuderparts striped, and the muzzle 

 greatly elongated. Mention was made of two strips of 

 skin, which iu due course reached England, and were 

 exhibited before the Zoological Society, when the animal 

 to which they pertained was definitely stated to be a new 

 species of zebra. On the 7th of April a coloured sketch 

 of the okapi was exhibited to the Society on behalf of Sir 

 Harry Johiistou. This sketch shows a hornless ruminant 

 with striped legs and uniformly coloured body. And it is 

 suggested by Sir Harry that the new animal may prove 

 to be a. near relative of Helladother/um of the Grecian 

 Tertiary. Be this as it may, the discovery promises to 

 be one of the highest importance, and the description of 

 the specimens reported to be on their way to this country 

 will be awaited with interest. 



Hctttrs. 



[The Editors do not hold themselves responsible for the opinions 

 or statements of correspondents.] 



STELLAK PAEALLAX. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — -As is well known the moon, although it revolves 

 round the earth, does not describe a circle in space but 

 a curve of double ciu-vature, because as it revolves round 

 the earth, the earth travels along its orbit round 

 the sun ; but the sun is travelling at a rapid rate 

 towards the star marked it in the constellation Hercules, 

 consequently the earth does not trace an ellipse in 

 space but a similar, double curve. But we are taught 

 at college that, when the earth's orbit is taken as base 

 line, in estimating the parallax of distant fixed stars, 

 the fixed star seems to revolve in a very small ellipse 

 corresponding to the orbital base line described round 

 the sun by the earth. 



How is this, when the earth really describes in space 

 a double curve, and how is the extra length of the bsise 

 line through solar translation estimated in calculating 

 the parallax of fixed stars ? W. W. Strickland. 



[There is no difficulty in principle in distinguishing 

 between the effect upon the apparent place of a star 

 of the earth's motion every year in its orbit round the 

 sun and the motion of the solar system in space. Thus, 

 if we observe the place of a given star on the same date 

 in several successive years, these places would be entirely 

 unaffected by the annual parallax, and the " proper 



motion " of the star could bo learnt from them. Obser- 

 vations at any other dates could bo corrected for this 

 " proper motion,' leaving the effect of the parallax 

 outstanding. The effects of precession, of the " sun's 

 way '' and of any actual motion in space which an 

 individual star may itself have, arc necessarily cumu- 

 lative, and go on increasing from year to year; the 

 effect of parallax is periodic, and runs through its 

 changes in the course of a year. — E. Walter Maunder.] 



SUNSPOTS AND TERRESTRIAL TEMPERATURE. 



TO THF. EDITORS 01<" KNOWLEDGE. 



Sirs, — -Will you kindly allow me space to assure Mr. 

 Quonsel that he is in error in attributing a connection 

 between sunspots and terrestrial temperature. Your 

 correspondent obviously cannot have road up the neces- 

 sary series of meteorological observations for the past 

 forty years, which refer to a large tract of the earfcli's 

 surface. Mr. Quensel makes no mention of the places 

 where the obsci'vations necessary for his deductions 

 were made. Are we to infer that his remarks arc 

 applicable to the continents of Europe, Asia, Africa, 

 America and Australia? Has he obtained a "mean" 

 temperature from these continents, and then compared 

 it with the sunspofc ciu-ve? Certain it is that up to the 

 present time we have ahxalutehj no evidence that there 

 is the ghost of a connection between the phenomena of 

 sunspots and terrestrial temperature. 



Louth, Lines. G. McKenzie Knight. 



[Mr. Maunder has already pointed out thai Mr. 

 Queusel's statement could not be accepted without the 

 figures on which it was based, and we think a similar 

 remark would apply to the assertion made by Mr. 

 Knight. The subject is a difficult one, and it is eviclciit 

 that much more analysis of the observations is rccjuircd 

 before any satisfactory conclusions can be drawn. It 

 must be remembered that the variation of sunspots is 

 only one of the indications of varying solar activity, and 

 that sunspot phenomena alone, therefore, need not 

 necessarily indicate the whole change of solar radia- 

 tion. — Eds.] 



CLOUDS ON MARS. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, Allow n;c to correct a mistake of mine made 



accidentally iu my letter published in Knowledge for 

 April. The word " dark " in tho letter should have been 

 " light." In the above letter I tried to call attention to 

 the antagonistic views of Mr. Thomas R. Waring to those 

 of other astronomers as to the visibility of clouds on 

 Mars. As I understand Mr. Waring he states that the 

 atmosphere of Mars is entirely free from clouds, and if 

 so, I should be pleased to know his opinion as to tho 

 natm-e of the " light-coloured, moving spots " to which 

 reference is made by Messrs. Wells and Gregory and 

 other authors who might be quoted. 



E. Lloyd Jones. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs —In your April issue Mr. Lloyd Jones says that 

 in a book by Mr. H. G. Wells and myself, " Honours 

 Physiography " (1893), " it is stated that Mars possesses 

 clouds which are visible in the large telescopes as dark 

 moving patches." I have pointed out to Mr. Jones that 

 no statement a.s to "dark" cloud markings is made in 

 the book, and I should be glad if you would make this 

 disclaimer known. What is said is that Cloud-like 



