8o 



NA TURE 



[May 26, 1 88 1 



The two sets of seeds were thus in exactly simUar conditions, 

 except for the increased atmospheric pressure and the compres- 

 sion of the atmosphere in the one case as compared with tlie 

 other. The following was the course of development : — By 

 9 a.m. of the 9th three of the seeds under the 2j atmospheres of 

 pressure had protruded their radicles, and this protrusion by 12 

 p.m. of the same day had become considerable, while as yet 

 there was no indication of commencing germination in any of 

 the seeds of the second set. By 10 a.m. of the loth the-e latter 

 had just begun to germinate, the radicles of the seeds under 

 high pressure being at the time a fourth and a third of an inch 

 long. 



Henceforward, however, the rapidity of development was 

 reversed. The seeds, under ordinary pressure, grew rapidly, 

 and their cotyledons became of a deep green colour ; while the 

 development of those under the high pressure became permanently 

 arrested and the cotyledons of one that had entirely escaped from 

 the seed-coats remained as etiolated as though they had been 

 grown in absolute darkness. 



They were allowed to remain untouched for eight days, when, 

 as there was no change, the bottle was removed from the tube 

 and simply allowed to stand inverted in the place it had formerly 

 occupied. The two— out of the five— seeds which had hitherto 

 remained unchanged novv rapidly germinated, and grew into 

 vigorous green young plants. 



Does a greatly increased atmospheric pressure or a greatly 

 coinpressed air prevent the development of chlorophyfl, and 

 while it stimulates germination does it prevent growth ? 



Liverpool, April 27 William Carter 



[This is an interesting observation, and seems to suggest a 

 new and comparatively unworked field of investigation — the 

 effect of different amounts of atmospheric pressure on plant-life. 

 With regard to the decomposition in the presence of chlorophyll 

 and under the influence of sunlight, of carbon dioxide, it is 

 remarked by Deherain ("Cours de Qiimie agricole," pp. 25, 

 26) that the conditions are analogous to those affecting the com- 

 bustion of phosphorus. This is not luminous in pure oxvgen at 

 ordinary pressure, but becomes sj immediately the oxygen is 

 diluted with nitrogen or hydrogen, and still more when the pres- 

 sure IS much diminished. Boussingault has shown that leaves will 

 not decompose pure CO„ at the ordinary atmospheric pressure ; 

 but a small cherry-laurel leaf placed in the pure gas decomposed 

 a cubic centimetre of it at a pressure of •I7m. (ComU. raid 

 1865, t. Ix. p. 872.)] ^ 



The Magnetic Survey of Missouri 

 It may interest some of your readers to know that, although 

 our State Legislature absolutely refused to do anything to aid in 

 the Magnetic Survey of Missouri, refusing by a "crushing" 

 vote even to authorise county ofiicers to have a true meridian 

 established, the work will still go on. A gentleman of St. Louis, 

 whose name is withheld at his own request, has assumed the 

 entire expense, and we shall now begin a more minute examina- 

 tion of the Missouri, Grand, and Osage valleys. We shall here- 

 l !f^^^' ''^ wagon, and shall do the work where it is most 

 needed in order to disclose the real directions of the isogenic 

 ""*=^- F. E. NiPHER 



An Optical Illusion 



The illusion described by Mr. Wilson and commented on in 

 an editorial note is anything but a novel one. An apparatus for 

 tlie experiment was purchased by the Birmingham and Midland 

 Institute, along with a quantity of optical apparatus, from Mr. 

 Kobert Addams, in, I think, 1857. Within the last few years I 

 have not^iced that the experiment is described and explained in 

 Friestleys "Light and Vision." I am writing from home, or 

 would give the exact reference. C. T. Woodward 



Cambridge, May 23 



I SHOULD like to know whether the following is a general 

 experience, or only a peculiarity of my own vision? 



If I stand with a source of li^ht — a lamp or a window — at one 

 side of my head, so that the light falls strongly on one eye only, 

 and look, successively or simultaneously, at the images of a piece 

 of white paper as seen by my two eyes, the image seen by the 

 eye next the light is greenish white, and that seen by the eye 

 farthest from it is light buff 



If instead of white paper I use the gilt ed,'es of a book, the 



image seen by the eye next the light is of a beautiful golden 

 green ; the other is of a brassy yellow, almost orange. 



This phenomenon does not appear to depend on any effect of 

 dazzling, for the experiment succeeds perfectly with very mode- 

 rate degrees of illumination. Joseph John Mijrphy 



Old Forge, Dunmurry, co. Antrim, May 23 



The Speaking Tube Anticipated? 



Has the foil iwing appeared anywhere in this connection as 

 yet, or not? If mt, please allow it to appear in Nature with 

 this qualification only, that the italics are mine. 



Describing the " speaking trumpets or pipes w-hich ran, we 

 are told, along the whole length of the Wall," Bruce says (" The 

 Roman Wall," by the Rev. John CoUingwood Bruce, p 76), 

 that Drayton long ago sang of them as follows in his 

 " Polyolbiou" : — 



" Townes stood upon my length, where garrisons were laid 

 Their limits to defend : and for my greater aid 

 With turrets I was built, where sentinels plac'd 

 To watch upon the Pict : to me my makers grac'd 

 With hollinv pipes of brasse, along vie still they ivctit. 

 By which they in one fort still to another sent 

 By speahin^ in the same to tell them what to doe, 

 jri nd socfj-om sea to sea could I be whispered through," 



Ashton-under-Lyme, May 17 



J. C. Shenstone. — A caseof Phyllody of thecalyx. " Ranun- 

 o//(7<rc(? particularly liable to this change" (Master's "Teratology," 

 p. 246 ; recorded in Anemone nemorosa, ibid. p. 252). 



ORIGIN OF THE ENGLISH MILE 1 

 T T is known that the mile of 1609 metres long passed 

 •*■ among English geographers and navigators as being 

 the length of the terrestrial arc of i' ; in other words they 

 made the degree equal to 60 of these miles. In reality it 

 contains 69'5 ; there is thus an error of about one-sixth. 

 This error, if it existed long among our neighbours, which 

 1 do not know, must have caused many a shipwreck. It 

 has had another very remarkable result ; it nipped in the 

 bud the discovery of the law of universal attraction. The 

 first time that Newton's great idea presented itself to his 

 mind the proof failed him. because he made use of the 

 common English mile to calculate the radius of the earth. 

 He renounced the idea for a long time, and only took the 

 calculation up again when he learned the results of 

 Picard's measurement of a degree in France. Whence 

 comes this defective estimate ? Certainly it does not 

 proceed from any effective measurement, for the worst 

 degree measurements, among those which have been 

 really made, and not fictitious measurements, like that of 

 Posidonius, are far from presenting errors of such magni- 

 tude. English geographers then must have committed 

 some mistake in taking their mile from ancient documents. 

 So long as navigation was limited to the waters of the 

 Mediten-anean, and to coasting along the western shores 

 of Europe, it was scarcely necessary to trouble about the 

 value of this element ; but from the time that the dis- 

 coveries of the Spaniards and Portuguese opened out a 

 much vaster field, sailors were compelled to make some 

 inquiry into the matter. I suppose that the English 

 navigators applied to their geographers, and that these 

 found nothing better to consult than Ptolemy, the great, 

 the only authority in these matters. But Ptolemy himself 

 refers to Eratosthenes ; he says that he verified the 

 measurements of the latter and found the same result, 

 viz. 500 stadia for the terrestrial degree. I have thus 

 been led to examine the measurement of Eratosthenes. 

 According to the documents which historians have pre- 

 served, Eratosthenes measured the great arc of meridian 

 which separates the parallels of Syene and Alexandria, 

 and finally found 700 stadia to the degree. This is how 

 he w-orked : — He observed at Alexandria, certainly by 

 means of a gnomon, the zenith distance of the sun at 



■ P.tper read at tha Paris Academy of Sciences by M. Faye (Compies 

 -endiis, xcii. Ko. 17). 



