Januaey 1, 1890.] 



KNOWLEDGE 



55 



value. Whether, however, the plan of mdicating the 

 accentuation of teclmical names by diacritical marks and 

 division into syllalilcs is nlto.ijether an advisnble one we are 

 not fully assured. 



I'loin'r-Licnd : mi hitniilurtlnii t<i liutninj. Y>y Rokkrt 

 Fisher. M.A. (Bemrose & Sons.) This is an enlarsenient 

 of a book which the author issued last year under the same 

 name, and which met with a sufficiently favourable re- 

 ception to tempt him to add to it a second and more 

 advanced part. The present volume gives an excellent 

 outline of Phanerogamic Botany in the simplest possible 

 style and language. The technicalities which usually form 

 so deterrent a feature in a first book on botany are, in the 

 introductory part, smoothed over in a v'onderful way, and 

 the reader is only gradually introduced to a fuller ter- 

 minology. The book is profusely illustrated with excellent 

 cuts, and there is a constant appeal to nature, and to actual 

 specimens to be hunted up fi'om hedges, woods, and fields, 

 that tends to check the acquisition of mere book-know- 

 ledge, and puts the tyro on the right path to become a 

 practical and scientific botanist, should his inclinations 

 travel in that direction. Young beginners in botany 

 could not start with a better ecjuipment than Mr. Fisher's 

 " Flower-Land." 



On the Causes, IVentiiniit, mul Ciirf <if Stoiiiiiicrhvi. By 

 A. G. Bernard, M.R.C.S., L.Ii.C'.P. (.T. .C: A. Churchill). 

 According to the author, at least one in every thousand of 

 the population of this country is a stammerer, but he is 

 connnced that this proportion is needlessly great, and that 

 persons so afflicted have in their own hands the power of 

 cure. He was once an inveterate stammerer himself, but 

 cured himf:2lf by the system he advocates in this manual. 

 There arc rules to be observed and exercises consisting of 

 literary extracts and sets of words difficult of pronunciation 

 to be repeated. Patience, perseverance, strict adherence 

 to the rules^ and careful practice of the exercises will, Mr. 

 P>ernard believes, produce in those suffering from this un- 

 pleasant defect proper control of the vocal organs, and 

 enable them to speak without discomfort to themselves or 

 their auditors. 



ILcttfVS. 



[The Editcir (iocs not hold himself responsible for \\\o opinions or 

 statements of correspondents,] 



liAUNAlU)'.^ COMKT (188+. 11.). 

 'I'd the Kditiir III' Knowledge. 

 Sill, in case anyone should think I ought to have in- 

 (.•huled this comet amongst those " due in ISOO," perhajjs I 

 may be allowed to point out the hopelessness of seeing it 

 ai the forthcoming return. Herr A. Jierberich has pub- 

 lished in the AKtnniomisi-he Xnrhrirhtrn, Nos. 2i)HH-i), a 

 very elaborate determination of its orbit, and finds that a 

 perihelion passage will be due on the 10th of next month 

 (.lanuary 1890); but he adds that the longitude of the 

 perihelion is :-50()°, whilst that of the sun at the time will 

 be 290", and that the comet's angular distance from the 

 sun, as seen from the earth, will scarcely exceed 9 " during 

 several months. At the following return, in the month of 

 May 1K95, the conditions of visibility will be somewhat 

 uu)rc favourable. The author of " the " Astroiumiical 

 ("ohunn " in Xntiire for October '2, ISSl, pointed out that 

 this comet nmst have made a near ajiproach to the planet 

 Mars in the month of April IHGH ; this may of course have 

 somewhat altered the period, and possibly it nuiy after all 

 be found that the comet is identical with be Vice's 



periodical comet of 1844, and with La Hive's comet of 

 1G78, determined by Le Verrier to be elliptic and of short 

 period. Yours faithfullv. 



P.lackheath, Dec. 11. W. T. Lvxs. 



P.S. — It has been pointed out to me that I ovei'looked, 

 in my article, the investigation of the orbit of Mr. 

 Denning's comet, which was published by Dr. B. 

 Matthiessen of Carlsruhe, ui Ast. Xcuhr., No. 2903. 

 Availing himself of an observation made at Strasburg 

 on the 24th of November 1881, five days later than any 

 previously published and used in the calculation, he 

 found the probable period to be a little shorter than Mr. 

 W. F. Plummer had done, and to amount to about 8'69 

 years, which would bring the comet to perihelion again in 

 the mouth of May 1890, though the theoretical brilliancy 

 will then be less than a third part ot what it was when 

 the comet was discovered by Mr. Denning in October 1881. 



WILSON'S THEORY OF SUN'SPOTS. 

 To the Kilitor it/ Knowledge. 



Sir, — It is with great diffidence that I venture to express 

 an opinion somewhat adverse to the statement of such a 

 well-known observer of solar phenomena as the Rev. Mr. 

 Hewlett, which is contained in his letter published in the 

 September number of Kno^nxedge, and is to the effect that 

 the Wilsonian theory of spots bemg depressions in the 

 atmosphere is wrong. Certainly, on looking over st;veral 

 drawings of sunspots that I have from time to time made, 

 my sketches of spots near the limb do not bear out Wilson's 

 idea. 1 find, in fact, that no hard and fast line can be 

 drawn respecting the appearance of a spot at the edge of 

 the disc. One spot, for instance, which I observed not far 

 from the F. limb, on .July 9, 1881, had the penumbra 

 arranged symmetrically round it during its progress across 

 the sun's surface until .July 17th, on which date it was 

 about as far from the \\ . limb as it was from the E. limb 

 when first seen. Its appearance now confirmed \Vilson"s 

 theory, ior much more of the penumbra was visible on the 

 fiiUiiiiinij side of the nucleus than on the ineceiUmi side. 

 From this instance, which I might illustrate with one or 

 two others, it appears to me that, just as Carrington was 

 of opinion that there were two kinds of solar .spots, " those 

 which notably change their place on the sun's surface, and 

 tliose which remain constantly at the same place," so we 

 must conclude iliat there are spots considerably depressed 

 below the level of the sun's surface, as well as those 

 (perhaps the larger number) which are but slightly, if at 

 all, depressed below the surlace. It would be interesting to 

 note whether the spectroscope reveaLs any difference in the 

 nature of the spots that could be accounted for on the sup- 

 position that they diti'er in depth. — Yours faithfullv. 



Forest Gate, F. B. .1. Hiii-Kixs. 



[The spots so frequently change in lorm as they pass 

 across the disc, that one must not assume too ivadiiv that 

 all changes of form on approaching the limb are due to 

 perspective. — Ed.] 



THE FACE OF THE SKY FOR JANUARY, 



By Hekbeht Sadler, F.R.A.S. 



W11I;NF\'FH the state of the sky during the 

 past month has permitted the sun's disc 

 being observed, the spots seen have been 

 both few in number and small in size. Con- 

 veniently observable minima of Algol (c/'. 

 "Face of the Sky " for December ISSS) occur at 9h. 

 48m. P.M. on the 8rd ; 6h 87m. p.m. on the 6th; llh. 



