March 27, 1902] 



NA TURE 



497 



are separated by shallow water, but towards the south the depths 

 increase to nearly a thousand fathoms. Atolls are found in all 

 stages of formation, including specimens of greater simplicity 

 than have been found anywhere except on the Yucatan plateau. 

 A preliminar)' report of the work will be issued as soon as the 

 charts are completed. 



Ix a paper published by the .\msterdam Academy of Sciences, 

 Prof. Eugene Dubois discusses the supply of sodiumand chlorine 

 by rivers to the sea. A large number of analyses of river-water 

 are dealt with, and Prof. Dubois arrives at the conclusion that 

 Sir John Murray's estimate of the amount of sodium delivered 

 by rivers is much too high. The point is of special interest in 

 relation to the attempts of Prof. Joly and others to estimate the 

 age of the earth from chemical denudation. Prof. Dubois' re- 

 sults seem to indicate a period of the same order as that 

 obtained by Lord Kelvin — twenty-four millions of years. 



Mr. J. Barclay, Birmingham, asks for an explanation of 

 an effect he has observed, produced by refraction of air. While 

 looking at a bookcase through the heated air rising from the 

 chimney of a lighted lamp, the line of sight being a few inches 

 above the top of the chimney, he noticed that one of the 

 volumes appeared to project in front of the row in which it 

 stood. Mr. E. Edser, to whom the observation has been 

 referfed, writes in reply: — "The illusion is obviously due to 

 the refraction of light by a cylindrical column of heated air, 

 which acts as a divergent cylindrical] lens. The refractive 

 index of the air of the room may be taken, roughly, as equal 

 to I '0003. If the heated air rising from the chimney of the 

 lamp has a temperature of 300° C, its refractive index would, 

 roughly, be equal to 1-00015. A' the interface between the 

 cold and heated air, the effective refractive index would be equal 

 to o'99985. Assuming the lamp chimney (and therefore the 

 column of heated air) to have a diameter of I inch, then the 

 focal length of the cylindrical lens would be o'oooi5. The 

 distance of the book from the lamp was about S feet, or 

 (say) 100 inches. Seen through the column of heated air, the 

 distance v of the book from the lamp is given by the 

 equation l/a - l/loo = 0-00015, '•'O"'' which v is found to be 

 99 inches. The book thus appears about an inch in front of 

 its true position, as observed by Mr. Barclay." 



We congratulate our Norwegian contemporary, Naltiren, on 

 having completed the first quarter of a century of its struggle for 

 existence in a country of only two and a quarter millions of 

 inhabitants. It is published in Bergen, where it was founded in 

 1877 by Dr. Hans Reu?ch, then an assistant in the Geological 

 Survey of Norway, of which he is now director. In spite of 

 many difficulties, Naturen gradually gained ground at a time 

 when old and excellent journals such as Tidskrifl for poptilaere 

 fremstillinger and Naturen og niennesiet (both published in 

 Denmark) were discontinued. In iSSi Dr. Reusch went abroad 

 for some years and handed over Natiiren to Herr Carl Kraft, 

 who conducted it on the same lines and against the same 

 difficulties until 18^6. In January 1S87 the journal became the 

 property of the Museum in Bergen, which continued its publica- 

 tion under the editorship of its director, Dr. I. Brunchorst, and 

 in 1S93 it received a yearly Government grant of Kr. 1000 

 (= 55/. lOf. 30'.), on condition that 400 copies are supplied 

 monthly at half price to State schools and public libraries, so 

 that poorly paid teachers and others in remote districts may 

 have access to its pages. In its first number for 1902, in which 

 it celebrates the commencement of the twenty-sixth year of its 

 existence, we are presented with the portraits of its first 

 two editors. The number also contains articles by the three 

 contributors to its first number in 1877, ^'i^- Dr. H. Reusch, Herr 

 I. Sparre Schneider and Prof. Geelmuyden. We wish the journal 

 a long and prosperous life. 



NO, 1 69 1, VOL. 65] 



In a lecture lately delivered before the Norwegian Geograph- 

 ical Society by Captain R. Amundsen, the author gave an 

 account of the proposed exploring expedition to the magnetic 

 North Pole. Captain Amundsen was first officer of the Belgica, 

 which sailed for the Antarctic in August 1897 with the view of 

 determining the exact locality of the magnetic South Pole, and it 

 was while that ship lay fixed in the drift-ice west of Graham 

 Land that the idea was conceived of exploring the magnetic 

 North Pole. For the contemplated expedition, the Gjoa, one 

 of the strongest and best sailing-vessels of the Arctic fleet, has 

 been purchased at Tromso. In 1831, Sir James Clark Ros 

 reached a position where the dipping-needle was only deflected 

 one minute from an absolutely vertical position, but the question 

 has been raised whether the magnetic pole is actually only a 

 point or whether the peculiarity of the needle assuming a 

 vertical position extends over a large area, and, further, whether 

 the magnetic pole changes its position. With the object of solving 

 these two questions, Captain Amundsen will sail in the spring 

 of 1903. The Gjiia is to be fitted with a petroleum engine and 

 will carry a crew of seven men. A travelling magnetometer is 

 under construction at the Deutsche Seewarte, and will resemble 

 that used on board the Fram. A dipping-needle is being con- 

 structed in London, and will be examined at the observatory of 

 the National Physical Laboratory. It is proposed to take 

 magnetic observations as frequently as practicable, to leave the 

 ship either at Matty Island or King William Land, and as soon 

 as the severest part of the winter is over to continue the journey 

 with the sledges to the place on Boothia reached by Ross. 



We have received a copy of Mr. C. E. Stromeyer's paper on 

 explosions of steam pipes due to water-hammers, read before 

 the Manchester Literary and Philosophical Society. The paper 

 deals both with the causes of these explosions and with the 

 forces which come into play when they occur. At the meeting 

 Mr. Stromeyer made two sets of experiments with water in glass 

 pipes. The first illustrated those accidents which are caused 

 when the steam pipes are so arranged that water may find a 

 lodgment over the boiler stop valve. When opening this valve, 

 the steam pressure shoots the plug of water along the pipe until it 

 strikes and shatters the engine stop valve, if this happens to be 

 left partly open. The other experiment showed that if near the 

 boiler stop valve there is an L pipe in which water can lodge 

 while steam is in the main pipe above the vertical leg, then by 

 draining away this water, which has, of course, to be done before 

 starting the engine, steam is admitted to the horizontal leg and 

 most violent steam-hammer blows occur, which have been the 

 cause of many explosions. In the theoretical part of the paper, 

 Mr. Stromeyer gives a proof that the velocity of a pressure 

 wave is the same as the velocity of sound, which has an impor- 

 tant bearing as showing that both undulatory and angular sound 

 waves travel with the same speed. Then as regards the pressure 

 exerted by an elastic body like water when it suddenly comes to 

 rest, he explained that a pressure wave travels from the front end 

 of the water column to the back end, and that the back end, or 

 in fact any part of the water column, continues to move forward 

 with its original velocity as long as it does not feel the wave of 

 pressure. The arrested (pressed) water column is, therefore, 

 shorter than the moving one. The ratio of the amount of 

 shortening to total length is the ratio of original velocity 

 (V) of the whole column to the pressure velocity (W). By 

 multiplying this ratio by the elasticity of water (E) we 



V 

 get the pressure P = E — . Thus a plug of water only 6 inches 



long propelled through a distance of only 2 feet under a pres- 

 sure of 15 pounds would on being suddenly arrested exert a 

 pressure of 6400 pounds. 



