160 



KNOWLEDGE 



[July 1, 1898. 





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A very ingenious contrivance has lately been devised by 

 Mr. Edwin Edser, a.r.c.s., and Mr. C. P. Butler, a.r.c.s., 

 ■which may be utilized for the purpose of facilitating the 

 reduction of prismatic spectra in terms of wave-lengths. 

 Two pieces of plate-glass, each thinly silvered on one 

 surface, are arranged with 

 these surfaces parallel and 

 nearly in contact. This 

 simple combination is ad- 

 justed in front of the slit of 

 a spectrometer, so that a 

 ray of slightly convergent 

 white light, when passed 

 through, gives a spectrum 

 consisting of white bauds 

 separated by dark intervals 

 due to the interference of 

 the direct ray with that 

 twice internally reflected. 

 If the wave-lengths corre- 

 sponding to any two inter- 

 ference bands be known, 

 that corresponding to any 

 other band can be calculated 

 or determined graphically 

 with extreme accuracy. In 

 order to adjust for parallel- 

 ism, a spot of light, or the 

 filament of a glow lamp, is 

 viewed through the silvered 

 surfaces. A long train of 

 images, of course, is visible, 

 and these must be brought 

 into coincidence. If a so- 

 dium flame is now viewed 

 through the air film, inter- 

 ference bands appear, which 

 must be regulated by pres- 

 sure to a maximum width, 

 an arc lamp being employed 

 for illuminating the colli- 

 mator slit. The chief ad- 

 vantage of this system of 

 caUbrating spectra consists 

 in the enormous saving of 

 time which it will effect. A 

 simple graphic method thus 

 serves to determine wave- 

 lengths — corresponding to 

 an immense number of spec- 

 tral lines —by mere inspec- 

 tion. When once the ob- 

 server has photographed 

 the spectrum, with the 

 accompanying scale, all he has to do is to index the scale, 

 and then he can commit it to the care of an ordinary 

 attendant devoid of scientific knowledge, who may perform 

 the reductions mechanically, in a manner somewhat 

 comparable to the way in which a carpenter measures his 

 boards and planks. 



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Comparison Scale for reduction of 

 Spectra. 



Crypton, or the " hidden stuff," is the name given by 

 Prof. Ramsay to the recently discovered atmospheric 

 element — a gas — the existence of which was suspected 

 when argon was eliminated from air three years ago. The 

 principal lines of the spectrum of crypton are green and 

 yellow, but although heavier than argon ics atomic weight 

 has not yet been worked out. Minute in quantity, it was 



at first exceedingly difficult to obtain air in suflSciently 

 large volumes as to reveal any appreciable trace of the 

 new gas. Thanks, however, to Prof. Dewar — who can now 

 supply gallons of air, in the liquid form, within the com- 

 pass of a test-tube — in the hands of Prof. Ramsay the 

 potency of liquid air as an instrument of research has 

 been manifested, and one of the first chemial products 

 obtained by its aid is, it would appear, nothing less than 

 a new element ! Its proportion in the air is about one in 

 twenty thousand. The brilliant yellow-green is believed 

 by Sir Wm. Huggins to be identical with the green auroral 

 line. 



" The Microbe in Agriculture " forms the subject of an 

 article in the June Number of the Nineteenth Century by 

 Dr. Aikman, in which he dwells at some length on nitirif/in* 

 and more particularly alinite — a pure culture of the bacillus 

 mefiHtlurium — designed for inoculating the soil with nitrogen- 

 fixing bacteria. He says : " When we reflect that in a 

 phial barely a couple of inches in length, and less than a 

 quarter of an inch in diameter, there may be contained the 

 means of enriching an acre of ground in its most valuable 

 of all fertilizing constituents, we realize the great advantage 

 such a process possesses over the more costly and trouble- 

 some mode of strewing large quantities of artificial 

 manure." It would appear that a system of co-operation 

 obtains among these minute soil workers. While some 

 are instrumental in initiating the first stages of decom- 

 position, others carry on its development through succes- 

 sive stages, and the microbic inhabitants of the soil are 

 classified according to the nature of the products they give 

 rise to. 



Messrs. Seeley & Co. will shortly publish a short popular 

 account of wireless telegraphy by Mr. Richard Kerr. It 

 explains in simple language the methods devised by Mr. 

 Preece, Signor Marconi, Dr. Oliver Lodge, and others who 

 have worked on this marvellous discovery. Mr. Preece 

 will contribute a preface. 



SELF-IRRIGATION IN PLANTS. 



By the Rev. Alex. S. Wilson, m.a., b.sc. 



ABSORPTION of water in terrestrial plants takes 

 place almost exclusively through the roots ; very 

 little of the rain or dew that falls on the foliage 

 finds its way into the interior of a plant directly 

 through the leaves or other aiirial parts. The 

 bark of the stem and branches prevents loss of water by 

 evaporation ; so does the impervious cuticle which covers 

 the leaves ; but any covering which hinders the passage of 

 water outwards must necessarily offer a corresponding 

 resistance to the entrance of water. For this reason those 

 portions of their surface which plants expose to the air 

 are, as a whole, ill adapted for imbibition. The freshening 

 effect observed when the leaves of a parched plant are 

 damped, arises not so much from absorption as from 

 diminished evaporation ; the water supplied by the roots 

 to the leaves does not escape so rapidly, and the leaf-cells 

 are in consequence kept distended. 



Quite other conditions obtain in plants which grow 

 submerged in water ; the cuticle is but slightly developed, 

 and imbibition takes place through the general surface. 

 Aquatics accordingly quickly dry up and shrivel when 



* See Knowledge, Vol. XX., p. 201. 



