180 



♦ KNOWLEDGE ♦ 



[Feb. 27, 1885, 



circulation as would malie its revolutions in the million years one 

 more or less than these 131 ! 



Of course, the minute change of 5, or even of 1, per cent., in the 

 rate of any of the first four arguments' movements, would utterly 

 change the whole table's character — double, perliaps, some maxima, 

 and turn others into minima ! 



After adding to his " Sept Planetes Principales," a few years 

 later, a heavier than all but two of them— yea, heavier than the 

 aggregate of all its five inferiors, of course, Levcrrier, could little 

 think of undertaking such a task as repeating all this for tlie sixty- 

 four inequalities of all the eight ! Will any one ever think it worth 

 while ? Not, I should say, unless with some grounds for thinking 

 the list of colossal planets (the Jupiter-Neptune class) complete. 

 A single addition must, hke that of Neptune, make all antecedent 

 reckonings as vain as these. It is not, observe, that Mr. CroU had 

 to add an eighth inequality merely to the seven he has taken ; but 

 each of those seven is separately revolutionised, both in magnitude 

 and period. 



Moreover, it is not as an eighth added to seven, but a third 

 added to hvo — the third heaviest of four (formerly three) that 

 Neptune enters. His task, Leverrier found much eased by the 

 insignificance of our four little inner planets in face of what ho 

 supposed the three big ones. Those he treated first by themselves 

 as a " syst^me qui est independaut des autres planetes " (p. 46). 

 But not independent, he soon found, of Neptune ! Each of those 

 that he treated as having but three of these inequalities, he would 

 now have to reckon subject to four ; and then treat the four 

 interior as each subject to eight. He tabulated the elements of 

 these (pp. Gl, 6G) on the then theory (of no Neptune), but no 

 further than to lOO.COO years, past and future ; and, of course, 

 would have been the last, I suppose, to have now assigned those 

 reckonings any value beyond the 10,000. The earth's orbit's 

 eccentricity, probably now below its average (though that is not 

 certain), will continue decreasing for between twenty and thirty 

 thousand years, to a minimum possibly as low as 'OOI; and in 

 another 20,000 rise again to about its present value. Further than 

 that, Levcrrier would certainly have denied that a single figure of 

 Croll's and your tables is worth the good vermin-killing arsenic or 

 lead of its ink. E. L. Garbett. 



P.S. — To show how utterly superseded and worthless, even had 

 Neptune never hecn found, their great author must latterly have 

 held the data whereon Croll's table (p. 123) is based, it may 

 suflice to quote this from p. 23 of the " Momoire," as printed in 

 1815, but calculated in 1839 :— 



"Si les qnantites /(, /i', ft- . . . qui representent les erreurs 

 possibles des masses etaient considerables, la determination des 

 variations qu'elles pcnrraient introduire dans les coefficients que 

 nous venous de calculer [i.e., all those Croll has used] serait presque 

 impracticable. Mais il est au contraire tres vraisemblable que ces 

 corrections ne sent que des petites fractions des masses admises 

 aujourd'hui [1839J, qu'ainsi pour Jupiter, /(' est au-dessous de 

 •002; que pour Saturne, /i^ ne depasse pas 'Ol ; que pour Venus, 

 la Terre et Mars, n}, fi-, et ;i^ ne depassent pas 'Ol. Les masses de 

 Mercure et d'Uranus seules presentent une grande incertitude, et il 

 ne^ serait pas impossible que ;t ne put s'elever a -\, et /i"^ a ^\„ on 

 meme plus." 



Now, in only two cases, Venus and Saturn, have the amendments 

 he found necessary in the " Annates de I'Observatoire" been 

 within the limits he had thus anticipated as possible. The denomi- 

 nator of Jupiter's mass, 1,050, which was not to err 2 thousandths, 

 has risen in Chambers's " Astronomy " (on Leverrier's authority) 

 to 1,040. That of the earth's mass, not to err beyond 4 per cent., 

 he soon made from 356,354 into 314,000 — a change above 13 per 

 cent. ("Ann. de I'Obs.," 1858). That of Mars, limited to the same 

 possible error, falls 12 per cent., from 2,680,387 to 2,994,790 

 ("Annales," 1861). That of Mercury, which he reckoned as 

 1,909,706, which "ne serait pas impossible" to err by a third, he 

 had to lower by three steps, finally to 5,300,000 ! And the denomi- 

 nator of mass of Uranus, which might have to be altered a /e«/?i, 

 " on meme plus," falls from his 17,918 to 24,899 in Chambers, or 

 leas than Ihrce-qunrtcr.i thereof. 



Even had his elaborate corrections then been applied (which 

 none have), and were there no AVji(iuic, I should deny that we have 

 the slightest knowledge whether the terrestrial eccentricity, say 

 50,000 years ago, was increasing or decreasing, or that one maximum 

 or minimum in this table can teach us more than if the whole had 

 come from shaking a lottery-bag. E. L. G. 



" WHAT MAN HAS DONE.' 



[1615] — I hold it important that nothing that has been done 

 should be stamped by the editor of Knowleoke as impossible. 

 Lately, sir, yon spoke of looking through a refractor at the sun " of 

 course, with a smoked glass." That, of course, is otioso. In May, 



An oculist told me I had gone 



1845, at 11 a.m., I, being then thirteen, in lat. 54° N., looked 

 steadily at the sun through a glass (2-in. object-glass, if I 

 remember rightly ; it showed Jupiter's satellites well in all 

 unclouded weather) surveying the spots, &c. I cannot say how 

 long — perhaps ten secouds. I had no pain or other inconvenience 

 after, and that eye is now keener than the other. I cannot under- 

 stand how I escaped ; the more as Socrates remarks in the 

 " Phaxlo," that those who look direct at the ccZijj.scrf sun, instead of 

 at his image in still water, lose their sight. This shows, by the 

 way, that smoked or coloured glass was not used, though Socrates 

 .'■■peaks (in the Clouds) of burning-glasses, and a darkened glass is 

 smipler than a lens. 



In Jan. 1877, 1 glimpsed a 

 star at about .c in this dia- 

 gram of the face of Taurus. 

 I have tried hundreds of 

 times since, but never saw it 

 again till last month, and a 

 few nights ago.* It must be 

 a telescopic ; or is it a vai'i- 

 able, with long period ? I 

 should be much interested if 

 you would tell me of what 

 magnitude it is. 



In 1864, a friend showed 

 me a page of the Times pho- 

 tographed in carte de rititc 

 size. I at once read four 

 lines of the first leader, 

 quite fluently; but was there 

 stopped by an intense pain 

 in both eyes. I find that 

 the height of the letters 

 would be one-sixth of that 

 of the leader type of the Times. 

 very near blindness. 



I am delighted you have taken up the question of bad type. I 

 have long thought severe legislation, prohibiting small type alto- 

 gether, can alone save our posterity's eyesight. I find my sight 

 failing now; your correspondence type wearies me even in strong 

 daylight; italics I find inuch harder than Roman letters, and Greek 

 more trying than these. MS. I find perfectly easy to read, which 

 I should not h.ave expected. From these data, were I to bring in a 

 Bill, I should propose to print Greek books in Roman letters (as 

 was often done in the middle ages ; they used Greek letters for non- 

 Greek tongues also), to prohibit the use of any type below, say, that 

 of your principal articles, and, above all, to cease the printing of 

 notes and extracts in smaller type. The eye has to change its 

 focus; this practice is the most trying of all printer's devilries, 

 save the American one of beginning an article in decent type, and 

 screwing you up, line by line, to a sort only half as large, 



I reported to you once that, in March, 1881, I had, aided by a 

 globular nimbus, seen Venus as a crescent with the naked eye. Yoti 

 replied in an early number of Kxowleuge that it was impossible ; 

 but I am as certain it was true vision as I am of my boyish feai 

 with the sun, which I know must seem to most appropriate to 

 Apollo chiefly on the hoie side. H.\llyards. 



[I am wholly unable to recognise the aeterism drawn by 

 " Hallyards." If, by the aid of a star atlas, he will letter the 

 principal stars in the group, I may be able to tell him something 

 about his J'. — Ed.] 



FORECASTING THE WEATHER. 



[1616] — Under the above heading there appear, in an Almanack 

 distinguished for the amount and value of its information, certain 

 remarks which I think are incorrect. They appear to have been 

 written by a member of a weather-oiEce, and have remained 

 unaltered for the last nine or ten years. 



They begin thus : — " Depressions on the surface of the great 

 aerial ocean surrounding the globe are marked by the barometer." 



Now, the " great aerial ocean," or, in plain language, the atmo- 

 sphere, is subject to the laws of gravitation, like all other matter. 

 It is densest at the surface of the earth, and becomes more and 

 more attenuated the higher we go, till it finally disappears. It, 

 therefore, has no surface, and can have no depressions. 



The barometer merely measures the weight of the atmosphere. 



The writer in the Almanack apparently does not know the 

 reasons why the atmosphere is so much lighter during gales of 

 wind and storms of rain, and so much heavier during the prevalence 

 of fine weather and light airs. 



He then informs us that storms travel with a velocity varying 



* Not with direct vision, but aa an undoubted fact, and more so 

 than in 1877. 



