September, 1902.] 



KNOWLEDGE 



209 



tliat this .should be imdertakeii even in fui'e of the iucom- 

 j.reheusihle fate whieh has hitherto decreed tliat the first 

 attempt at a new route or method of exploration in the 

 Arctic regions is always more successful than auy subse- 

 quent endeavour on the same lines. 



Dr. Nanseu has somethini; to say with regard to the 

 interesting question of the climate of the Arctic regions in 

 past geological periods. He points out thai the super- 

 ficial layer of light cold water exercises a cooling influence 

 on the atmosphere in several ways. If any cliange had 

 occuri-ed in the courses of the great Siberian and American 

 rivers, diverting their water from the Polar Basin, or any 

 change in the configuration or depth of the basin itself, 

 the cold surface layer might also have disappeared. A 

 raising of the sea-level by 1000 metres would admit a far 

 greater volume of warm Atlantic water and mitigate the 

 climate to a very marked degree, a fall of the sea-level by 

 even 500 metres would produce a still more ]>ronounced 

 effect in the opposite direction, and there is evidence that 

 such changes have occurred in the past Thus Dr. 

 Nansen's results aft'ord fresh data for attacking the semi- 

 fossil problem of the cause of glacial periods. 



After the perusal of a memoir so full of new facts and 

 far-reaching suggestions, we come as a sort of anti-climax 

 to a paper on " Hydrometers and the Surface Tension of 

 Liipiids," which is included in the volume. The subject 

 is of importance, because hydrometers have had much to 

 do with ascertaining the facts as to the salinity, not of the 

 North Polar Basin alone, but of all parts of the ocean. It 

 IS a (juestion full of difticulty, on which there exists a 

 considerable literature, and about which controversies of 

 some intensity have arisen. Dr. Nansen traces the bad 

 reputation of the ordinary hydrometer to the caj>ricious 

 variations of surface tension in liquids which have been 

 contaminated by any greasy substance, and he describes a 

 series of experiments resulting in a method of skimming 

 and cleansing the surface, which enables a hydrometer to 

 be used with more certainty of a good result than was 

 before considered possible. We believe that with care in 

 the >ise of ungreased water-bottles, clean utensils, and 

 freijuently-washed hands, surface tension may not prove 

 so formidable a variable as Dr. Nansen's experiments seem 

 to suggest. However, there is no doubt that the use of 

 the stemless or total immersion hydrometer recommended 

 by Dr Nansen promises to simplify the labour, and to 

 improve the accuracy of density determinations at sea. 

 He jiroposes to employ a set of cylindrical hydrometers 

 without stems, one of which, having a specific gravity 

 very near that of the sample of water to be tested, is 

 immersed in it, the containing jar being constructed with a 

 vacuum jacket on Professor Devvar's principle. A delicate 

 thennometer is also immersed in the water, and the 

 temperature is raised or lowered by stirring with a closed 

 glass tube containing ice, or a similar tube containing 

 warm water, until the float is in exact equilibriimi with 

 the water. The only reading I'eijuired is that of the 

 tem])erature, as the weight, volume, and expansibility of 

 the hydrometer have been previously ascertained. 



Tliere is still a great future before oceanography. 

 Every year demonstrates more clearly the intimate relation 

 between the temperature cf the sea surface and climate, 

 and such works as this prove that the temperature of 

 the sea surface can only be understood by the investi- 

 gation of the conditions of the mass of the water at all 

 depths. In some parts of his investigations Dr Nansen 

 introduces mathematical treatment, which is now fairly 

 justified by the improved data available for discussion, 

 and we would commend some of the problems touched 

 upon to the tutors of Cambridge as not unworthy of 

 their attention. 



STUDIES IN THE BRITISH FLORA. 



By R. Llotd Praeger, b.a. 

 v.— ON AN IRISH BOG. 

 Leaving the comity road, we strike down a bohereen— a 

 " roadling," to use the English equivalent — towards where 

 the brown edge of the peat bog rises a couple of fields 

 away. On one side of the lane is a broad ditch of still 

 brown peat water, which the sloping sunlight brightens to 

 a rich amber. The ]iatches of brown-leaved Potamoijeton 

 colunitiis which grow below the surface harmonize well 

 with the dominating tint of water and soil; and in startling 

 contrast to these the light strikes on cloud-like masses of 

 Chara frau'lii', bere quite free from limy iucru.station, and 

 vivid in their greenness. On the other hand, flat peaty 

 meadows extend, full of Yellow-Kattlc and Aijrostisvitlyaris. 

 The Orchids like this ground, and amid the pink and red 

 sjjikes of 0. maculata and incamata, we see the greeny 

 white of Habenaria chloroleuca and H. bifolia, and the 

 fragrant purple pyramids of H conopsea. More sparingly, 

 in a drier spot, is a colony of the beautiful Bee Orchis 

 (Ophiys apifera), and the little Frog Orchis (H. riridis). 

 AVe pass to a flat expanse of almost bare peat, where 

 Agrostis vulgaris and Riimex Acetosella are only just ob- 

 taining a hold, and Senecio sylvaficus shifts about season 

 bv season. This ground is used for drying and stacking 

 the peat after it has been cut from the neighbouring bank. 

 The cutting is done somewhat irregularly, and we sur- 

 mount several successive steps, and rising some fifteen 

 feet, find ourselves on the heathy surface of the bog. This 

 portion has slipped and shrunk owing to the drainage 

 induced by the turf-cutting ; and while the Ling appears 

 benefited by the change, most of the plants look starved, 

 and the little pools are all dry. So we push upward and 

 onward through the heath. Soon brilliant patches of 

 Bog-moss, or Sphaguiim — green, yellow and crimson — make 

 their appearance, the surface pools are filled with water 

 and fringed with Sundews, the cultivated land is lost to 

 sight behind us. A couple of stunted Birches, Ihe only 

 break in the sky-line in front of us, give something to 

 steer for. A Curlew rises with a loud whistle. We pause, 

 as the Ijubbling water reminds us at every step that we 

 are now beyond the influence of turf-cutting and drainage, 

 to examine the flora at leisure. 



The plants which form the vegetation here constitute a 

 very distinct association ; very homogeneous, too, though 

 limited in variety. Wander as we will, we scarcely 

 enlarge the plant-list formed in our minds by our first 

 scrutinising glance. The dominating species, and the one 

 which gives the general surface its appearance and colour, 

 is the Ling, Calhina Erica. With it, in smaller quantity, 

 is the Bell-heather, Erica Tetralix. The great green and 

 red cushions of Sphaguum form a conspicuous feature. Two 

 other ericaceous plants, Andromeda Polifolia and the Cran- 

 berry, Vaccinium Oxycoccus, ap]iear to like the shelter and 

 cool dampness which those mosses afford ; their struggling 

 stems wind far into the dej)ths of the Sjihagiiiim, while 

 their leaves and flowers brighten its surface. Great grey 

 cushions of a drier nature are formed here and there by 

 another moss, Rhacomitriam lanuginosum ; some of these 

 rise three feet above the general surface of the bog. 

 Almost as abundant as the Ling are two other plants, 

 the beautiful little Bog Asphodel, Narthecium ossifraguin, 

 with its golden stiirs of blossom and Iris-like leaves, 

 and the Club-rush Scirptts cvupitosrM, growing in tufts 

 with stiff radiating stems, like glorified pin-cushions. 

 Both the Cotton-grasses, Eriophorum angustifolium and 

 E. vafiinatiim, are here, though sparingly, and that quaint 

 erect little plant, looking strangely out of place, is the 

 Fir Club-moss, Lycopodium iielago. The oozy sinuous 



