56 



• KNOWLEDGE 



[Jan. 16, 1885. 



difficulty. Our author says in his preface, " My especial 

 object has been to illustrate the direct application of the 

 laws of motion, and thereby to produce a treatise of an 

 elementary character, but of educational utility to the 

 student ^yho is commencing the s-tudy of theoretical 

 kinetics." He may fairly claim to have succeeded. 



The Sieye of London. By " Posteritas." (London : 

 Wyman i- Sons. 18S.5). — Some years ago, a work entitled 

 the " Battle of Dorking " created a considerable sensation, 

 in showing how vulnerable these islands were to foreign 

 invasion. Following upon similar lines, "Posteritas" 

 prophetically indicates the outcome of our present (so-Ciilled) 

 "Liberal" policy, and describes a French invasion of 

 England aad the siege of the Metropolis. Not unmindful 

 of the strategy which led to the disaster of Islandwhaua, 

 and of the tactics of Maiwand and Majuba Hill, we would 

 yet fain believe that the crass stupidity with which our 

 author credits the British military authorities is — to use a 

 mild term — exaggerated. Nevertheless, in the words of 

 the old proverb, " There is many a true word spoken in 

 jest," and this little book contains hints by which even the 

 Dii majorrs of the Horse Guards and the Admiralty may 

 conceivably profit. SI vis pacem, para helium. 



Differential Calculus for Berjinn-ers. By Alexander 

 Knox, B. A., Cantab. (London : Macmillan i Co. 1884.) — 

 This is, without exception, the best book for the very be- 

 ginner in the differential calculus that we have ever met 

 with ; that lete-noire of the incipient student, the diflferential 

 co-efficient, Vjeing made intelligible ia a manner which is as 

 novel as it is ingenious and effective. Mr. Knox's mere 

 notion of rendering the geometrical idea of points and lines 

 easily apprehensible by means of coloured rectangles of 

 paper, of itself shows how thoroughly he grasps the little 

 difficulties which beset the beginner. We stall be strangely 

 surprised if the circulation of this tiny volume is not very 

 large indeed. 



Factors in Algehra discovered by Arrangement, Trial, 

 and Si/mmetrt/, icith Applications. By Eev. J. G. Easton, 

 M.A (London : Groombridge it Sons. ISSi.) — Here is 

 another useful book for a beginner, who all but invariably 

 finds a difficulty in factorising an algebraical expression of 

 the slightest complexity. Beginning with the easiest cases, 

 Mr. Easton gradually leads the student on through a series 

 of increasing difficulty. Not to speak irreverently, fac- 

 torising is to no small extent a natter of " dodges," and in 

 these our author is paiticularly strong. His book will be 

 found valuable by the incipient algebraist, whom it may 

 and will save many a five or ten minutes' weary and 

 purposeless pondering. 



W/tat is lielifjioni By C. X. Annotated by Robert 

 Lewins, M.D. (London ; W. Stewart i Co. 1883.)— 

 Into the theological portion of this curious pamphlet we 

 will not, and into its metaphysical part we need not, enter. 

 Here we have the Ego and the non-Ego once more warmed 

 up. Briefly, the L^niverse must be held to consist of the 

 sum of Dr. Lewins's sensations, We seem to have heard 

 something remarkably like this before. 



Brass Repousse. By Madame Amehe. (London : Pub- 

 lished by the author.) — In simple language, illustrated by 

 well-executed and intelligible wood-cuts, Madame Amelie 

 gives directions for the production of that brass repousse 

 work which has recently been resuscitated. Ladies who 

 require a novel, interesting, and artistic form of recreation 

 will find it in the practice of the art so plainly described 

 in the little work before us. 



We have also on our table The Journal of Botany, The 

 Anierimn Xaturalist, The Medico-Legal Journal, Heath's 

 Fern Portfolio, The Medical I'ress and Circular, Bradstreefs, 

 The Tricyclist, and Society. 



THE FACE OF THE SKY. 



Fbom Jan. 10 lo Jan. 30. 

 By F.E.A.S. 



TIIE usual daily examination of the Sun for spots and facuUt- 

 will be made, whenever the weather permits. The aspect of 

 the nisrht sky is shown in Map I. of " The Stars in their Seasons." 

 Both Mercury and Venus continue to be most unfavourably placed 

 for the observer. Mars is invisible. Jnpiter — to the east of 

 Leonis, and travelling towards Regulus — is by far the most brilliant 

 and conspicuous object in the night sky, and he and the phenonena 

 of his satellites supply the young observer with a series of the most 

 nteresting and instructive sights. Of such phenomena occurrinsr 

 at convenient hours during the next fortnight, the following are 

 the chief: — On the 18th, Satellite I. will disappear in eclipse at 

 lOh. 46m. 463. p.m., and the shadow of Satellite II. enter on to 

 Jupiter's face eight minutes after midnight. On the 19th, the 

 ingress of the shadow of Satellite I. will take place at 8 p.m., but 

 it is doubtful whether it will be visible, as Jupiter will be so low- 

 down. The transit of Satellite I. itself begins at Sh. 42m. p.m. ; 

 the egress of its shadow at lOh. 20m. p.m. ; and that of the satellite 

 at llh. 2m. On the 20th, under unfavourable conditions, Satellite I. 

 will re-appear from occnltation at 8h. 1.3m. p.m. ; as will Satellite 

 II., later on, at llh. 15m. p.m. On the 22nd, Satellite III. will 

 enter on to Jupiter's face at 7h. 58m. p.m. ; though here again it is 

 doubtful whether it will be seen to do so. Its shadow will pass off 

 his opposite Urab at 9h. Im p.m. ; while Satellite III. itself will 

 not follow it until llh. 33m. p.m. This transit shonld be care- 

 fully watched to see whether the Satellite shows as a light or a 

 dark spot on the disc of the planet, or changes from one to the 

 other. On the 2oth, the egress of Satellite IV., which will occur 

 at 9h. 40m., should be observed for the same reason. On the 26th. 

 the shadow of Satellite I. begins its transit across the planet at 

 9h. 54ai. p.m. ; followed by the Satellite casting it at lOh. 2Sm. p.m. 

 The shadow leaves Jupiter's opposite limb at 12h. 14m. p.m., and 

 the Satellite at 12h. 47m. p.m. On the 27th. with Jupiter close to 

 the horizon, SatelUte I. wUl be eclipsed at 7h. Sm. 25s. p.m., as will 

 (under more favourable circumstances) Satellite II. at 9h. 33m. Is. 

 p.m. Satellite I. will reappear f»om behind the body of the planet 

 at 9h. 58™. p.m., Satellite II. not until the next morning. Perhaps 

 Satellite I. may be seen to leave Jupiter's disc at 7h. 13m. p.m. on 

 the 2Sth, an observation which applies to the egress of the shadow 

 of Satellite II. at 6h. 54m. the next evening. Later on the 29th the 

 egress of Satellite II. occurs at 7h. 34m. p.m., the ingress of the 

 shadow of Satellite III. at 9h. 19m. p.m., and that of Satellite III. 

 itself at llh. 19m. p.m. Its shadow leaves Jupiter's opposite limb 

 at 12h. 59m. p.m. Saturn continues in an excellent position for the 

 observer, and to repay all the attention that can be given to the 

 scnitiny of his marvellous system. He continues to form a 

 rudely isosceles triangle with /3 and J Tatiri, as stated a fortnight 

 ago on p. 15. Uranus has not yet arrived in a favourable position 

 for the amateur, and, as we have so often said recently. Neptune 

 can only be picked up as a small, dull, fixed star by fishing in that 

 blank part of the sky to the .S.S.E. of c and ? Arietis. The Moon 

 was new at 8h. 3u'5m. this morning, will enter her first quarter at 

 Ih. 20-3m. a.m. on the 24th, and be full on the 30th at 4h. 19-2m. 

 in the afternoon. Several occultations will occur at convenient 

 hours during the next fourteen days, all of the stars, however, being 

 small ones. On the 21st, B.A.C. 57, of the 6ith magnitude will 

 disappear at the dark limb of the Moon at 5h. 39m. p.m., at 

 an angle of 144° from her vertex, reappearing at her bright limb 

 at 61'. 52m. p.m. at an angle from her vertex of 309°. On the 22nd 

 c Piscium, a 5^th mag. star, disappears at the dark limb at 

 5h. 33ni. p.m. at a vertical angle of 112^. It reappears at the 

 bright limb at 6h. 47m. p.m. at an angle of 324° from the vertex of 

 the Moon. On the 26th, B.A.C, 1526, a star of the Cth mag., dis- 

 appears at the dark limb at 7h. 13m. p.m. at an angle from the 

 vertex of 19°; to reappear at the bright limb at 7h. 49m. p.m. at a 

 vertical angle of 328°. On the 27th the disappearance of the 6ith 

 mag. star B.A.C. 1930 happens at the dark limb of the Moon at 

 Sh. 38m. p.m. at an angle of 33° from her vertex: its reappear- 

 ance at her bright limb at 9h. 30m. p.m. at an angle from her 

 vertex of 316°. Lastly, on the 30th, B.A.C. 3122, of the 6ith magni- 

 tude, will disappear at the Moon's bright limb at 8h. 54m. p.m. at a 

 vertical angle of 30'; to reappear at her dark limb (very close 

 indeed, though, to what is seemingly a bright one) at 9h. 59m. p.m., 

 at an angle of 237° from her vertex. The Moon leaves Sagittarius 

 for Capricornus at 2 o'clock this afternoon, travels through the 

 latter constellation during the day and night, and at 9 o'clock to- 

 morrow morning enters Aquarius. She actually occupies until 

 2h. p.m. on the 20th in her passage across the whole width of 

 Aquarius, and it is not until the honr just named that she crosses 

 into Pisces. Exactly three days later, i.e.. at 2 p.m. on the 23rd, 



