us 



KNOWLEDGE. 



[July 1, 1899; 



mostly taking the form of irregular sinuous slits, although 

 tending to become cii-cular round the margins of the 

 pseudoscula. Velvet-sponges are inferior in value to the 

 ■wool-sponge, the best samples selling at about four shil- 

 lings and sixpence each. 



Before concluding this portion of the subject, a few 

 additional lines may be devoted to the distribution of the 

 Mediterranean sponges. On the east shore of the Adriatic, 



FlQ. 5. — Velvet-Sponge. Hippospongia equina tneandrina. 

 West Indies. 



and the coast of Greece from Trieste to the Bay of Nauplia, 

 it appears that only the elephant's-ear-sponge is met with. 

 From Nauplia and Candia to Eritra, on the coast of Asia 

 Minor, both the Turkey toilet and the Zimocca sponge are 

 met with. Except oflf Cyprus, where the latter does not 

 grow, the Turkey toilet, the Zimocca, and the bath-sponge 

 are met with from Eritra to Tripoli. West of the latter 

 place the Zimocca disappears ; the bath and Turkey alone 

 extendmg from TripoU to Tunisia, and the former, as 

 already said, being represented by a coarse variety known 

 as gerbis, in the Strait of Gibraltar. The limitation of the 

 Turkey cups to the seas east of Malta has been already 

 referred to. 



Many years ago the head-quarters of the sponge-trade 

 were located at Trieste ; subsequently they were trans- 

 ferred to Paris, whence they finally migrated to London, 

 the great bulk of the trade being in the hands of the 

 Messrs. Cresswell.* As regards the volume of the British 

 trade in this commodity, the following figures give the 

 amounts and values of the imports between the years 1862 

 and 1870, subsequently to which no returns were published 

 for a considerable period : — 



These figures indicate, on the whole, a progressive 

 annual increase in the amount of the imports, with very 

 considerable fluctuations in value. According to the 

 Board of Trade returns, the amount of the imports in 1897 

 was one million nine hundred and fifteen thousand and 

 seventy-five pounds, with a declared value of two hundred 

 and twenty-seven thousand two hundred and forty-six 

 pounds. The latter must, however, be regarded as only a 

 very rough approximation to the reality. As regards the 

 great excess in the amount of the imports over those given 

 in the foregoing table, it must be borne in mind that 

 during the former period the great bulk of the trade went 

 to foreign ports. In 1875, for example, the French im- 

 ports reached two hundred and forty-six thousand six 

 hundred and sixty-six kilogrammes, and two hundred and 

 fifty -seven thousand eight hundred and seventy -eight kilo- 

 grammes in the following year. It is accordingly quite 

 possible (although we have no data to go on) that the 

 total annual yield of sponge for the world's supply may 

 now be considerably less than formerly. 



As regards the dressing of raw sponges, it may be well 

 to mention that the so-called imbleached descriptions are 

 treated locally with a bath of weak sulphuric acid, by 

 which they are turned light brown. After being washed 

 in sea-water and sprinkled with sand to increase their 

 weight, they are packed in bales, and on arrival are sold 

 in this condition. On the other hand, the bleached 

 sponges arrive in this country in the raw condition, 

 stowed in bags, and pressed flat. After a good macera- 

 tion in Condy's fluid, they are soaked and squeezed in 

 a solution of sodium hypo-sulphite and hydrochloric acid, 

 after which they are wrung, dried, sorted and trimmed. 

 Their lighter colour gives them a decided advantage 

 in appearance over the unbleached descriptions, but 

 there is the drawback that the strength of the fibre is 

 very slightly weakened by the processes to which they 

 have been subjected. 



* To tlie members of this firm the author's best thanks are clue for 

 much valuable information, and likewise for the specimens from 

 T^hicli the descriptions and figures are taken. 



THE ENERGY OF RONTGEN RAYS. 



By Dr. J. G. McPhebson, f.k.s.e.. Science Examiner in 

 the University of St. Andreiv's. 



SINCE the marvellous properties of the Rontgen rays 

 were discovered, very many experiments have been 

 made to bear upon their application to physiology 

 and surgery. Dr. PoUand's Atlas of the develop- 

 ment of the formation of the bones of the wrist 

 from birth till seventeen years of age is one of the most 

 startling of the recent successes of the process; and this has 

 overturned to some extent the old theory of the formation 

 of these bones. 



There has been, however, as yet but little done to deter- 

 mine the enerijy of these rays. The Rev. Alexander 

 Moflfat, B.sc, has been studying the subject in Erlangen, 

 and has submitted to the Royal Society of Edinburgh the 

 result of his investigations. 



A. Rotti was the first to attempt to determine the dura- 

 tion of the Rontgen rays. He used a Ruhmkorfi' coil with 

 a rotating interrupter to make and break the current in 

 the primary circuit. On the interrupter he mounted a 

 photographic plate, and in front of it had a screen of lead 

 with a slit in it. The Rontgen rays were made to pass 

 through the slit and make a photograh of it on the plate. 

 From the amount of broadening of the photograph he found 

 that the duration of a discharge was about -^^^ second. 



Dr. Trouton, of Liverpool, adopted the method of rota- 

 ting a zinc-toothed wheel between the Rontgen lamp and 



