Jan. 20, 1882.] 



• KNOWLEDGE • 



241 



AN ILLJL&XRATED 



MAGAZtNEo?S€IENCE^ ^ 

 P lainltWorded-Exactl IPescribed j 



LONDON: FRIDAY, JANUARY 20, 1882. 



Contexts of Ko. 12. 



Profawor Toung on the Sun 241 i 



Prwcssionof theEquinoiM. Bvthe ; 



Eilitor. With an lUustritivc 



Map %J3, j 



Seein? through the Hand. Br 



Thomas Foster .'. 21* | 



Intelligpnce in Animals 245 j 



Excavations At the Pyramids, By 



W. M. Flinders Petrie 246 



The Magic Wheel (UUilrated) 24" 



The Moon and the Weather. By II. 



A. BuUer 2« 



Something aliout the Potato 249 



The Purple of the Ancients ... 250 ] 



Meteoric Organisms. By Carl Vogt 251 ; 



PAGE 

 CoBBBSPOITDBycE : — Vegetarianism 

 — Communication ^vitn the Moou 

 —The Xautilus— Celestial Maps- 

 Cheap Telescopes — Sunlight on 

 Fires — Liquids and their Vapours 

 ^Botanical Contrivance — Marine 

 Boilers — The Descent of Man — 



Plating .Alkaloids, &c 251-255 



255 



Replies to Queries 



.\nswers to Correspondents 256 



Xote^on Art and Science 257 



Our Mathematical Column 258 



Our Whist Column 259 



Our Chess Column 259 



PROFESSOR YOUXG OX THE SUN. 



PROFESSOR YOUNG, although no one would imagine 

 it from the book before us, is one of those to whom we 

 owe some of the most impoi-tunt of tlie discoveries which, 

 during the last few years, have added so mucli to our 

 knowledge of the sun. It is well that we should have 

 treatises such as this from the workers themselves to whom 

 our knowledge is due. For, though the most skilful 

 observers are not always the ablest either in dealing with 

 known facts and deducing sound theories from them, or in 

 presenting them to the unscientific world, there is always 

 in their >vritings a special value and something of the 

 charm which v.e find in accounts of travel Ijy those 

 who have seen what they describe. Professor Young, 

 however, possesses much more than mere observing 

 skill. He is a sound and careful reasoner, and 

 if there is a certain terseness and preciseness (more than 

 mere precision) in his writing, which detracts a little 

 from its literary charm, this has probably been rendered 

 necessary by the limited nature of the space at his dis- 

 posal, and in no sense deprives his work of its claim to be 

 regarded as exceedingly well written. This treatise pos- 

 sesses also another quality, very important, we conceive, 

 in astronomical writing.* Professor Young is a mathe- 

 matician, and the formulas he gives, even when they are 

 not of his own devising, are given with adequate under- 

 standing of their meaning and value, which, unfortunately, 

 has not been the case with all the treatises on astronomy 

 recently published. 



Taking first Professor Young's treatment of the dimen- 

 sions, mass, and power of the sun, we note that he adopts 

 for the sun's distance an estimate very near that which 

 the labours of his countryman. Professor Newcomb, seem 

 to indicate as nearest to correctness, viz. : gijSS-'SiOOO 

 miles, with a probable error of about a quarter per cent, 

 or 22.5,000 miles. This would correspond with a mean 

 iquatorial horizontal solar parallax of 8"-80, or, in un- 

 technical terms, the earth seen from the sun at his mean 



^ " The Sun." By C. .\. Young, Professor of Astronoiny in the 

 College of New Jersey. (Messrs. Appleton & Co., Xew York.) 



distance, would have an apparent maximum diameter of 

 17""60 (about one 106th part of the apparent mean dia- 

 meter of the moon or of tlie sun as we see these orbs from 

 the earth.)* We may note in passing, that in comparing 

 the methods of determining the sun's distance by observa- 

 tions of Mars on the stellar heavens and of Venus in 

 transit. Professor Young omits to notice that whereas 

 the full displacement of Mars, as seen from difterent 

 parts of the earth, is available, the displacement of Venus 

 on the sun's disc is only a part of lier actual displace- 

 ment, the sun himself being displaced (roughly, only 

 about seven-tenths of the displacement of Venus is avail- 

 able). His account of the American photographic method 

 of observing the transit of Venus is full of interest, 

 though calculated to make Englishmen somewhat ashamed 

 of the relatively unscientific method which (despite good 

 advice to the contrary) was adopted at tlie English stations. 



The mass of the sun, deduced from this estimate of the 

 distance, is about 330,000 times that of the earth. 

 Expressing this in tons. Professor Young uses what we 

 take to be the erroneous Ameiican system of notation, 

 saying that the earth's mass amounts to about two octillions 

 of tons, where we should say two thousand trillions of 

 tons. Respecting the sun's attracti\-e power, as exerted 

 on the earth, Professor Young quotes the following im- 

 pressive illustration from a recent calculation by ilr. 

 Warring : — " We may imagine gravitation to cease, and to 

 be replaced by a material bond of some sort, holding the 

 earth to the sun, and keeping her in her orbit. If, now, we 

 suppose this connection to consist of a web of steel wires, 

 each as large as the heaviest telegraph wires used (No. 4), 

 then, to replace the sun's attraction, these wires would 

 have to cover the whole sunward hemisphere of our globe 

 about as thickly as blades of grass upon a lawni. It would 

 require nine to each square inch." 



It should be added, however, and still further enliances 

 our conceptions of the sun's might, that were the connec- 

 tion between the sun and earth of this nature — that is, by 

 steel wires — more than three hundred da3S would be re- 

 quired to make the pull of the sun felt at the earth. The 

 action of gravity is e.xerted certainly in less than a second. 

 In fact, the most careful observation of the planet's mo- 

 tions reveals no evidence that gravity takes even any 

 appreciable time at all in traversing the spaces separating 

 the various members of the solar system from each other. 

 This apparent iustantaneity of the action of gravity is one 

 of the greatest mystei-ies known to science. 



Sir John Herschel has well remarked that Giant Size 

 and Giant Strength are little without Giant Benevolence. 

 It is the light poured forth by the sun on the planets, the 

 heat whereby he nourishes them, more than his vast bulk 

 and his mighty mass which fit him to be the central ruler 



* " To borrow the curious illustration of Professor Mendenhall," 

 says Professor Younf,', " if we could imagine an infant witli an arm 

 long enough to enable him to touch the sun and bum himself, ho 

 would die of old age before the pain could reach him, since, acconl- 

 ing to the experiments of Helmholtz and others, a nervous sliock is 

 communicated only at the rate of about 100 feet per second, or 

 1,637 miles a day, and would need more than 150 years to make tlie 

 ioumey. Sound would do it in about 11 years if it could bo trans- 

 mitted through celestial .ipace, and a cannon-ball in about 9, if it 

 were to move uniformly with the same speed as when it left tUo 

 muzzle of the gun." These illustrations are striking — we have 

 seldom used them in lecturing on the sun without noticing thattlioy 

 produce a strong impression on the audience. But we find another 

 illustration in the book before us, still more impressive. While the 

 earth is travelling 20 miles along her circular path, her path 

 deviates from the tangent at the first point of the arc of 20 miles by 

 onlv one-eighth of an inch. This is the distance which the sun, 

 with all his tremendous attractive energy, draws the earth towards 

 him in a second of time. 



