Feb. 17, 1882.] 



KNOWLEDGE 



533 



ing every living thing as the offspriiig of a previous living 

 thiiJg, quite overthrown by considerations of tlie dinsity 

 air must have if it were as full of gmnis as they -eujiposecl. 

 Pasteur, Pallinger, and Tyndall have coniplett^ly de- 

 stroyed tliis argument, and shown that g6rn)S in vast 

 numbers can exist tloating in the air witliout any 

 appreciable addition to its weight, or obvious diminu- 

 tion of its transparency, though, as we slmll see, tliat 

 is easily aflected. Germs of various kinds are most 

 numerous in the air of towns and iuliabited rural districts. 

 They Ivcome fewer as mountainous lieiglit-s are ascended, and 

 in well-selected situations disapp.ar mtirely. All ordinary 

 air will cause life to appear in appropriate fluids that have 

 been previously rendered sterile ; b\it if a bottle containing 

 such a fluid is opened with due precautions on a jnoiuitain 

 peak, and then hermetically sealed, no life is developed. 

 In such experiments Pasteur used glass vessels with their 

 necks drawn out, and sealed up by melting them in a 

 spirit lamp, or witli a blow-pipe. To ensure against acci- 

 dentally introducing any germs lie might have carried with 

 him up tlie mount;iin, he broke the tips of the vessels' 

 necks with pliers made hot in a spirit lamp, and, after air 

 had been admitted, instantly closed them by reuieltiiig. He 

 thus found pure air to be free from any life-producing 

 particles. Tjnidal's experiments were made by imitating 

 the well-known motes in a sunbeam. He found that a 

 beam of electric light gave evidence of amazingly minute 

 particles floating in the air, and that when this effect 

 entirely ceased, the air contained no gemis. We can 

 seldom form an accurate idea of the real size of the 

 minutest objects we can just discern -with the microscope. 

 They often look a good deal bigger than they are, through 

 the optical defects of the instrument and the eye, though 

 Dr. Pigott found that when all the conditions can be 

 rendered favourable, the error is very small. The smallest 

 floating particles lit up by Tyndall's artificial sunbeam are 

 too minute for individual recognition bv the microscope. 

 It is only when they are numerous enough to form a delicate 

 cloud that tlieir presence can be made manifest. Objects 

 while floating in the air could not possibly be seen witli 

 high powers. It is necessary to collect tlicm, and keep 

 them either still, or onlj' moving in some fluid with mode- 

 rate velocity. If they are very nearly of the same refrac- 

 tive power and colour as the fluid in which they are 

 immersed, they can only with great difficulty be dis- 

 tinguished at all. Naturalists and physiologi-sts can 

 seldom arrange all the circumstances in the way 

 r-iost favourable for attaining to the extreme limits of 

 -ion, and their researches are u.sually made within much 

 irrower limits. If, however, the utmost possible power of 

 the microscope could always be employed, it would not 

 bring us near the prob.able limits of organic life. The 

 minute organisms capable of inducing changes analogous 

 to the fermentation caused by yeast have received great 

 attention of late years, and several important diseases are 

 distinctly traced to them. Bechamp estimated that eight 

 thousand millions of germs of one micro-ferment only 

 occupied one cubic ■2.')th of an inch. Not one of these 

 minute bodies could develope except by carrying on com- 

 plicated processes of a chemical nature, involving very 

 active movements of its atoms and molecules. 



The mathematicians have made calculations founded upon 

 the pressure exerted by gases, and other considerations, which 

 ( show that a particle of the sort of matter, such as albumen 

 and protoplasm, chiefly concerned in life processes, contains 

 in a space of one cubic thousandth of an inch more 

 molecules than any one could possibly form any conception 

 ot Sorby, taking a probable mean of such calculations, 

 supposes one cubic thousandth of an inch of water to 



contain 3,700,000,000,000,000 molecules. A sheet of 

 ordinary note paper is about one hundredth of an inch 

 thick. One tenth of this w ould, of course, be one-thousandth 

 of an iucli, and a little 6<iuare box of that size each way 

 would liold the amazing numbcj of water molecules 

 mentioned. Perhaps a few thousands of such molecules 

 may sutlice for .some manifesUvtiwi of life, but even if 

 many uiillions should be requisite for tlie structure of the 

 humblest and simplest germ, \v(j.<;puld oc-Vj^r jSxpect to see 



the actual beginnings of lifa ! i 



When one million is spoken of, few pea-sons form any 

 definite conception of the quantity iiu.ant, and billions, 

 trillions, quadrillions, ic, convey no graduated conceptions 

 to anybody except in the rougJiest wa)'. Mr. Samuel 

 Butler, in his work on " Unconscious Memory," states that 

 "a man counting as hard as he can repeat numbers one 

 after another, and never counting more th:m one hundred, 

 so that he shall have no long words to repeat, may, 

 perhaps, count ten thousand, or a hundretl a hundred 

 times over, in an hour. At this rate, counting night and 

 day, and allowing no time for rest or refreshment, he would 

 count one million in four days and four hours, or say in 

 four days only. To count a million a million times over 

 he would require four millions of days, and roughly ten 

 thousand years. For fi\o hundred millions of millions he 

 must have the utterly unimaginable period of Ave million 

 years.' And yet in how small a space the matter around 

 us contains molecules to this inconceivable extent ! The 

 things unseen far surpass in number, as in minuteness, tlie 

 things seen. 



THE LAST TRANSIT OF VEXUS.* 



Bv THE Editor. 



MY friend, our F.RA.S., used to say the transit of 

 Venus was, ^vith me, like King Charles's head with 

 Mr. Dick. The resemblance was certainly striking ; Mr. 

 Dick was always trying to keep King Charles's head out of 

 the Memorial, and constantly failed ; I spared no eflbrts 

 to bring the transit of Venus before the public, and 

 always succeeded. Be this as it may, it is certain that, 

 except in the case of an event like the transit, which was 

 bound to come ofl' at a particular time, mattirs of scientific 

 discussion are generally none the worse for waiting. Cer- 

 tainly, now that the transit is over, and no good can arise 

 from any discussion of the best ways of obser\ing it, I 

 should have thought myself very unlikely to go again over 

 the well-worn ground, or to recall the circumst;inces of a 

 long past controversy : is not tiw story told in the En- 

 cyclopiedia Britannica, in the American Cyclopa'dia, and in 

 the Monthly Notices of the Astronomical Society i 



But I must confess the introduction of the treatise 

 before us— a treatise giving ample evidence of the zeal 

 and energy with which Sir George Airy could do any work 

 to which he gave his mind— has somewliat changed my 

 views as to the desirability of silence. There is not a word 

 which is absolutely untrue in these pages ; but there is a 

 (luiet siif/yeHio fal^i, a calm and complete suppressio vert, 

 which I cannot" but consider ywr tropfort. Let me briefly 

 run through the facts of the case. 



In 18.")7, Sir George Airy made a communication to the 

 Astronomical Society, in which a comparison was made 

 between the transits of 1874 and 1882, with regard to the 

 suitability of the two chief methods for observing these 



• Account of "Observations of the Transit of Venus, 1874, 

 December 8. Printed for the Government Stationery Office under 

 the authority of the Lords Commissioners of the Treasury, 1»»1- 



