16 



KNOWLEDGE. 



[January 1, 1900. 



amount of atmosphere above each unit of the surface 

 here, that there is on the Moon. But this atmosphere 

 will be differently distributed. Half of our atmosphere 

 is passed through when we ascend 3i miles from the 

 earth's surface. To pass through half the Moon's at- 

 mosphere we should have to ascend 23 miles. At lOi 

 miles therefore above the surface of the two worlds we 

 should find the same amount of atmosjDherc above us in 

 both cases, and at 21J, miles the actual density of 

 the atmosphere woidd be as great for the Moon as for 

 our earth, though at the surface of the ground the pres- 

 sure at the earth's surface would be 37.6 times as great 

 as on the Moon. Above 21 J, miles high the entire ad- 

 vantage would rest with the Moon. Now the earth's 

 atmosphere is sufficiently dense far higher than this 

 to vaporize meteors by the resistance which it offers 

 to their path, and to produce strong crepuscular effects. 

 We have no evidence of an atmosphere approaching 

 this in efficiency, on the Moon. It seems clear then, 

 that the Moon has not, at pi'esent, the proportion of 

 atmosphere to which its mass entitles it. If it never 

 had more than at present we must agree with Mr. 

 Macgeoi'ge that " the theory of vegetable remains ne- 

 cessarily falls to the ground.'' But seeing how little 

 we know as to the condition and extent of the earth at 

 the time when the lunar crust had become solid and 

 cool, or of the distance apart of the two bodies at the 

 time, it is certainly rash to say that the Moon may not 

 then have had a respectable atmosphere. As to what 

 has become of it since, we most certainly cannot agree 

 with Mr. Macgeorge that " it is impossible that it 

 may have been attracted by the earth," nor is it " in- 

 conceivable that it may have been absorbed by the sub- 

 stance of the Moon." Neither hypothesis is, however, 

 necessary, for Dr. Johnstone Stoney's researches tend to 

 show that the Moon has not sufficient attractive force 

 to retain permanently an atmosphere of constituents 

 similar to those of our own ; and assuming that the 

 Moon once had a comparatively dense atmosphere, this 

 would necessarily fvilly explain its present disappear- 

 ance.] 



[Collecting Meteoric Dust. — Messrs. T. S. Overbury 

 and L. B. Booth enquire how the Rev. J. M. Bacon 

 collected meteoric dust by means of gun-cotton during 

 his recent balloon voyage to observe the Leonids. The 

 answer is of the simplest. A continuous current of 

 air was drawn thi'ough a tube in which a small plug 

 of gun-cotton was fixed, which would act as a filter to 

 filter I ut any dust which it might contain. The gun- 

 cotton could easily be dissolved at the end of the voy 

 age, and the amount and character of the dust which it 

 had taken up, if any, be ascertained. 



[E. 'Walter Maunder.] 



ACIDS IN SOIL. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — 'Will you be so good as to inform me if there 

 exist in any part of England or Ireland marshy soils, 

 or rather mineral moors, which contain besides sul- 

 phuret and peroxide of iron: — organic acids such as 

 formic acid or acidity, and if so in what proportion to 

 the other ine;redients. 



South Tottenham, 



Dec. 12th, 1899. 



W. A. Smith. 



Sir .1. William Dawson, whose death on 19th 

 November, 1899, we regret to record, was a leading 

 man of science of the old school — a teacher who stoutly 

 supported the final destiny of man as taught in Revela- 

 tion, and emphatically opposed to all theories of the 

 evolution of man from brute ancestors, nor would he 

 allow anything more than a moderate antiquity for 

 the species. Of Scottish extraction, he was born at 

 Pictou, Nova Scotia, in 1820, obtained the degree of 

 M.A. at Edinburgh in 1842, then recrossed the Atlan- 

 tic, and spent some time in scientific exploration under 

 Sir Charles Lyell's direction. Papers contributed to 

 the Geological Society of London soon brought him into 

 prominence. In 1855 he was appointed Principal of 

 McGill University, Montreal, only excelled in America 

 by that of Harvard, and the scientific side of that in- 

 stitution was practically Sir William's creation. The 

 Royal Society of London in 1862 elected him a fellow, 

 and twenty years later he received the Lyell Medal of 

 the Geological Society of London. In 1884 he was made a 

 K.C.M.G., in 1880 he discharged the duties of President 

 at the Birmingham Meeting of the British Association, 

 and he wa« the first President of the Royal Society of 

 Canada. Eozoon Canadense, described by him in 1865, 

 opened a controversy on organic life which is not yet 

 entirely disposed of. The study of Geology he would 

 have " delivered from that materialistic infidelity which, 

 by robbing nature of the spiritual element and of its 

 presiding Divinity, makes science dry, barren, and re- 

 pulsive." " Modern Science in Bible Lands," " Eden 

 Lost and Won, " among his many popular books, in- 

 dicate the trend of his teaching. Sir William's solid 

 contributions to science in the form of papers to learned 

 societies, periodicals, and magazines, were very numer- 

 ous, those to our own Royal Society numbering one 

 hundred and fifty-eight. 



Sir Henry Tate, whose death occurred on the 5th 

 December, 1899, will be remembered as a successful 

 man of business who utilised his great wealth in pro- 

 moting the interests of science and art. " This gallery 

 and sixty-five pictures were presented to the nation by 

 Henry Tate for the encouragement and development of 

 British Art, and as a thank-offering for a prosperous 

 business career of sixty years." So reads an inscription 

 affixed to the base of a column in the vestibule of the 

 magnificient pantheon of Art on the banks of the 

 Thames erected on the site of Millbank Prison. Sir 

 Henry endowed many scholarships, contributed £10,000 

 to the building fund of Owen's College, and donations 

 to the extent of some £50,000 to University College, 

 Liverpool. Born at Chorley, Lancashire, m 1819, he 

 served an apprenticeship to the grocery trade, and sub- 

 sequently engaged in sugar refining — a business which, 

 under his shrewd management, rapidly expanded to 

 gigantic proportions, and " Tate's cube sugar " became 

 a familiar object all the world over. As his wealth 

 augmented he freely utilised it in the stimulation of 

 education and in patronising artists. Previous to the 

 opening of the Academy Exhibition each year he gave 

 a great dinner at Park Hill, Streatham, to the leading 

 artists, and in course of time he acquired by purchase 

 a collection of the works of British Artists of the day, 

 which gradually led him up to the idea of forming a 

 permanent home or Gallery thoroughly representative 

 of British Art. He offered £80,000 to build a gallery, 

 provided the Government would give a site. Vacant 

 land near the Embankment at Blackfriars was declined 



