140 



KNOWLEDGE. 



[June 1, 180C. 



stone firmly fixed in the bed tbo waves move up stream, 

 though the head of the group cannot advance beyond the 

 stone. It often liappcng that tbo condition which pro- 

 duced tlie corrugation of the water surface is annulled, 

 leaving the group of waves still in existence, and the waves 

 continue to move up stream. It is then interesting to 

 note what happens to the first wave of the group which is 

 exposed to the action of a straight-forward current. It 

 continues to move up stream, the crest of water above and 

 the ridge of sand below ; but the sand ridgo becomes lower 

 and lower, its up-stream motion continuing, however, 

 until the ridge has been quite scoured away. The first 

 water wave has now disappeared, and the second sand 

 ridgo is exposed to the straight-forward current and 

 is in like manner scoured awav — persevering, however, to 

 the end in its up-stream motion. Thus the whole group 

 is obliterated, but for a time the sand ridges maintain the 

 corrugations on the surface of the water. It is also to the 

 sand waves, I believe, that the upstream motion of both 

 sand wave and water wave is due. We have here to do 

 with flying sand, as I have said, and flying sand is also 

 falling sand. There is a constant sand-rain falling 

 through the water, and it is often possible to see quantities 

 of sand dropping on the upper half of the weather slope of 

 the ridges. Of course, the sand does not drop vertically ; 

 it falls very obliquely, for the downward motion through 

 water is slow. Consider, then, as a first approximation, 

 that the sand-rain comes down obliquely in straight lines. 

 The weather slope of a sand hill, which is tilted up to 

 meet the shower, is of course more exposed to the shower 

 than the leeward slope ; so that when there is much flying 

 sand in the stream the sand ridge moves up stream, 

 carrying with it the water ridge. When the up-stream 

 ■waves extend the whole way across the channel, the path 

 of the sand particles may sometimes be seen to be curved 

 outward towards the edges of the stream, a motion which 

 seems to help in building up the ridges at their two ends, 

 and which probably assists to some extent the up-stream 

 motion. 



By examining the waves somewhat higher up the stream, 

 it is often possible to hit upon the position where the waves 

 are stationary ; still higher up one may sometimes see very 

 similar waves which are going down stream, in which the 

 shower of flying sand is not sufficiently dense to maintain 

 the ridges in place. 



A RARE METAL. 



By T. L. Phipson, Ph.D. 



AT the beginning of this century the great Swedish 

 chemist Berzelius discovered a new metal in 

 some Norwegian rocks, and dedicated it to the 

 mythological deity of the ancient Scandinavians, 

 the god Thor, by calling it thorium : the mineral 

 in which it was found was also called thorite. 



It was at a period at which great activity was manifested 

 in the search after new substances contained in rocks, 

 mmerals, and rare or precious stones. Chemists had not 

 jet made much way into the mysteries of the organic 

 world. They were not acquainted with the marvellous 

 products which have since been derived from plants ; 

 animal chemistry was very little known ; but a great 

 insight was being obtained into the nature of the con- 

 stituents of minerals, and ever since the middle of the 

 ei,i;htcenth century discoveries of new metals were being 

 made with astonishing rapidity, 



During this extremely interesting period of scientific 

 research, when men like Humpliry Davy, Lavoisier, 



Klaproth, and Berzelius vied with each other as dis- 

 coverers of the secrets of nature, considerable nu nber;! of 

 most curious substances were brought to light — metal; 

 which, to this day, are scarcely known, even by name, to 

 the general public, and are still little enough known, 

 indeed, to the mo-.t eminent of our modern chemists. 

 Cerium, for instance, was lound in a kind of granite rock 

 in Sweden, glucinium in the emerald and beryl, zirconium 

 in a precious stone I'rom the East called jargon, and 

 titanium in the black sand of some Cornish streams. 



When a new substance is thus discovered, the thought 

 that it may some day be applied to a useful purpose is 

 generally quite absent from the mind of the discoverer. 

 Ho is perfectly satisfied with the novelty of the discovery. 

 Only those who pass their existence in a laboratory devoted 

 to research can realize the intense interest with which 

 every new property of these rare curiosities is studied. 

 The book of nature is really more attractive than the 

 finest pages of the greatest writers, and as its secrets are 

 gradually revealed they rivet the attention more and more, 

 quite independently of the possible application of these 

 revelations to any particular art or industry. Neverthe- 

 less, it must be confessed that in these practical days such 

 considerations are not always so entirely absent from the 

 mind as they used to be. 



It is needless, perhaps, to say that, of all the new metals 

 which have come to light since the middle of the last 

 century, very few have come to any extent into daily use. 

 Hitherto, by far the most unpromising, perhaps, in this 

 respect, has been the metal thorium, And its oxide thuria. 

 It was found in a blac'c, shiny mineral, resembling 

 black glass, sticking in the Norwegian granite rocks, and 

 afterwards in a few other stones of various colours, where 

 its presence was thought to bo accidental. It possessed 

 no very striking properties. The oxide (thoria) is white, 

 and forms white salts with acids ; no colours are obtained 

 with it. In fact, it was no more interesting in its chemical 

 behaviour with other substances than common lime, to 

 which it bears a good deal of resemblance. But it was 

 very heavy, very infusible, and very rare ; and it was cer- 

 tainly quite distinct from any substance which the crust of 

 the earth had, as yet, yielded to the inquisitive searcher 

 after new metals. 



Thoria was first found combined with silica upon the 

 little island of Loeven. not far from the small town of 

 Brevig in Norway. It was discovered by a Swedish 

 diplomatist named Esmarck, and handed to his friend, the 

 chemist Berzelius, that he might analyze it and so find out 

 what it was. In making this analysis Berzelius soon 

 discovered that he was dealing with an entirely new 

 substance. Some time afterwards the same new substance 

 was found by the late Prof. Woehler, the celebrated chemist 

 of GiJttingen, and a pupil of Berzelius, in a stone from the 

 Ural Mountains called pyrochlore, which is also found in 

 Norway ; and more recently it has been met with iu another 

 rare mineral called monazite. 



It was soon seen to bo extremely difficult to smelt the 

 metal out of the oxide of thorium, as we get iron or copper 

 out of their oxides, by heating it to a very high temperature 

 with coal or charcoal. However, Berzelius did manage 

 to get out a minute quantity of the metal by other 

 means, and obtained it as a metallic powder, not unlike 

 lead in colour and appearance. He foimd that when 

 this metal was heated red-hot in the air it took fire, 

 and burnt with a most extraordinary brilliancy. The 

 light emitted was even more strikingly brilliant than that 

 produced by the combustion of magnesium, which is at 

 present so much used by photographers and makers of 

 fireworks. 



