f)() 



KNOWLEDGE 



[April 1, 1896. 



those of the subordinate series, and -which extends to 

 shorter wave-leugtbs." 



Elsewhere they write :" — " There is no instance of an 

 element whose spectrum contains two pairs of series 

 ending at the same place. This suggested to us the idea 

 that the two pairs of series belonged to different ilemonts. 

 . . . . We therefore believe the gas in clrveite to 

 consist of two, and not more than two constituents. 

 We propose to call only one of the constituents 

 helium — the one to which the bright yellow double 

 line " (D3) " belongs, whose spectrum altogether 

 is the stronger one — while the other constituent 

 ought to receive a new name." 



A very suitable name has been accordingly pro- 

 posed by Dr. .Tohnstone Stoney, and the second 

 element in clcveite gas is nowknownas "parlielium." 

 Further evidence that " helium " aud ''parhelium " 

 are really two distinct elements must form tbe 

 subject of another paper, in which it will also be 

 possible to glance at their different astronomical 

 relationships. 



seldom more than ten feet in girth. It is extremely hardy 

 and a rapid grower (especially the weeping variety), but does 

 not live to a very great age. One of the finest birches in 

 Scotland is represented in Fig. 1. It is about seventy feet 

 in height, with a girth of eleven feet four inches, and was 

 planted about seventy years ago on the banks of " bonnie 

 Doon." 



THE BIRCH. 



By George Paxton. 



" Most beautiful 

 Of forest trees, the Lady of the Woods." 



WELL does the birch {Betula alba) deserve 

 to be called "Queen of the Forest" 

 and " Lady of the Woods." No tree 

 is more generally admired on the 

 ground of its own intrinsic beauty : 

 the favourite of poet, painter, aud all lovers of 

 nature. It matters not whether it be seen in a 

 London square. Highland glen, or Lowland pasture; 

 the eye is at once arrested by its light and graceful 

 elegance. 



But perhaps all the beauties of a well-grown birch 

 are best brought out when the tree happens to be 

 of the weeping variety, growing beside aud over- 

 hanging still water. Then note and admire its 

 silvery stem, graceful drooping branches, and light 

 fragrant foliage, perhaps lit up by tbe rays of the 

 setting sun into festoons of pure gold ; the water 

 below reversing and doubling all ! Thus seen, on a quiet 

 autumn evening, the birch forms a picture that will linger 

 in the memory—" a thing of beauty and a joy for ever." 



With the poet Burns the birch, or birk, as he called it, 

 was chief favourite among trees, being mentioned in his 

 works no less than thirteen times. In the noblest and 

 most pathetic of all his poems, " To Mary in Heaven," 

 the place of last parting is described — 



" O'erhung with wild woods thiek'ning green ; 



The fragrant bircli, and hawthorn hoar 



Twin'd amorous round tlie raptur'd scene." 



Again he goes to meet his " ain kind dearie " — 



" Down by the burn, where seen ted birks 

 \Vi' dew are hanging clear. . . ." 



The birch is found in all the colder regions of Europe, 

 Asia, and America. It is common in this country, and a 

 true native of the British Isles. It is very abundant 

 throughout the whole of Eussia, and in Greenland it is 

 said to be " the only tree;" but there it is much diminished 

 in size, owing to the coldness of the chmate. In Britain 

 it grows to a height of about fifty feet, with a trunk 



* Nature, Sept. 26lh, 1895, 



near tlie "Auld J3ri'' o' Doon.' 



The tree is known at first sight by its silvery bark, small 

 leaves, and light and graceful form. The leaves are ovate, 

 and unequally serrated. (Fig. 2.) The flowers, in the 

 form of drooping catkins, appear in April and May. 



The fragrance to which reference has been made comes 

 from a kind of resin which exudes from the leaves and 

 young twigs, especially after rain or heavy dew. The 

 wood of the birch is tough, but not very durable. It is 

 used for making spoons and shoes chiefly in Russia, and 

 in France and Germany for carriage construction, 

 especially for the felloes of the wheels ; but its principal 

 use is for gunpowder charcoal. Tbe bark is remarkable 

 for its durability ; it is almost indestructible, and will 

 remain quite fresh long after the wood it has encircled 

 has rotted away. The ancient inhabitants of Britain 

 took advantage of this peculiarity and built their canoes 

 of birch-bark ; remains of these canoes have been 

 frequently dug up from the gravel banks of the River Clyde. 

 In Canada, birch-bark canoes are still used ; they are made 

 from a species known as the canoe or paper birch. 

 Portions of the smooth bark, ten to twelve feet long, are 

 stripped from the tree, stitched together with fibre, and the 

 seams coated with resin, thus making a very light boat. 



