August 14, 19 13] 



NATURE 



607 



extended by the author, who is director of the 

 Laboratory of Physiology and Technology of 

 Fermentations at Copenhagen. The new work is 

 a remodelling of the first edition, and due regard 

 has been paid throughout to the advancement of 

 this branch of applied science during the last 

 decade. The absence of an index is scarcely com- 

 pensated for by the somewhat full table of con- 

 tents. 



LETTERS TO THE EDITOR. 



[The Editor docs not hold himself responsible for 



opinions expressed by his correspondents. Neither 



can he undertake to return, or to correspond with 



the writers of. rejected manuscripts intended for 



this or any other part of Nature. No notice is 



taken of anonymous communications.] 



Variation of Mean Sea-Level. 



The many papers which have been written in recent 



years upon the above subject have dealt chiefly with 



the now well-known annual fluctuation (first noticed 



by Lord Kelvin nearly fifty years ago), by which the 



mean intertidal level of the sea stands on our North 



Sea and Baltic coasts something like 20 cm. higher in 



1900 1901 1902 1903 1906 1905 1906 1907 1908 '909 





Alean annual heights ol mean sea-ievel, 1900-9, con.pared wiih the mean lor 



the whole period. At Dundee. Mean of fourteen 



Danish and German ports, after Dr. Brehmer. 



autumn than in spring. But while we still know too 

 little about the details and the causes of this pheno- 

 menon, we know much less about the fluctuations of 

 longer period, or even of the elementary facts of 

 correspondence between different coasts in regard to 

 the mean level in successive years. 



A paper published a couple of months ago by Dr. 

 Brehmer, of Hamburg, in the Annalen do- Hydro- 

 graphie, gives a valuable set of data for the years 

 1900 to 1909, drawn from fourteen German and Danish 

 ports, from Bremerhaven to Memel. The results at I 

 NO. 2285, VOL. 91] 



all these ports are very concordant and all show a 

 remarkable elevation of mean sea-level in 1903. I 

 had lately been analysing the tide records at Dundee 

 (foi the years 1897-1912), and the correspond 

 the mean annual values at Dundee with Dr. Breh- 

 mer's observations, as the accompanying diagram 

 shows, is so remarkably close as to deserve particular 

 attention. Only between the years 1905-7, and 

 especially in tgo6, is there any noteworthy discrep- 

 ancy. D'Arcy W. Thompson. 

 August 1. 



On the Transmission of X-Rays through Metals. 



When a beam of X-rays is allowed to pass normally 

 through thin rolled metal sheets and fall upon a 

 photographic plate placed behind and parallel to the 

 sheet, some curious patterns are obtained. 



These patterns fall into two classes : (a), in which 

 the central spot produced by the direct beam is sur- 

 rounded by an irregular halo of smaller spots, and 

 (6), in which the central spot is surrounded by faint 

 extended patches forming a perfectly symmetrical 

 pattern. The design varies with the metal. 



Class (a) markings are given by metal sheets which 

 are either well aged or recently annealed, while the 

 symmetrical patterns of class (b) are only obtained 

 with newly rolled sheets. The spots of the former 

 are due to reflections from the microcrystals within 

 the metal, while the symmetrical patterns of the latter 

 are produced by the structure imparted to the metal in 

 passing through the rolls. These star-like patterns 

 are evidently analogous to those obtained when a 

 beam of light passes through a crystal which appears 

 streaky to the naked eye. By annealing a newly 

 rolled sheet the pattern changes from class (6) to 

 class (a) and vice vcrsA. 



It will be of interest to study the nature of the 

 structure which gives rise to the symmetrical patterns. 



H. B. Keene. 



University of Birmingham, August 7. 



A Red-water Phenomenon due to Euglena. 



A phenomenon of dichromatism in Euglena pre- 

 cisely similar to that described by Prof. Arthur Dendy 

 in Nature of August 7 was recorded by me in The 

 Essex Naturalist in 1890 as occurring at Donyland 

 Heath, near Colchester. During July and August the 

 surface of the largest pond on the heath was almost 

 completelv covered with a film which was red in the 

 morning and turned to green in the afternoon. I 

 watched the change take place on August 3 at noon, 

 the transformation taking about half an hour. The 

 omen of blood was viewed with some alarm by the 

 superstitious in the village, and was held to betoken 

 some ill for the community. After the heavy rains of 

 August the pond was quite clear of the film, and no 

 earthquake occurred. 



Dr. D. D. Cunningham mentions, in Science Gossip, 

 1886, a similar phenomenon in tanks around Calcutta. 



Colchester, August 8. Charles E. Benham. 



The Ribbon-Fish. 



A specimen of the rare, deep-sea ribbon-fish, 

 Trachyptcrus arcticus, which was landed at the 

 Grimsby market recently, has been sent to me. The 

 following details of the specimen are perhaps worth 

 reporting : — Length, 5 ft. 8§ in. ; greatest width, 

 ro| in. No anal or pelvic fins. Caudal fin not axial, 

 and the ventral portion without fin rays. Base of 

 pectoral fin horizontal. Dorsal fin with 154 smooth 

 rays. Teeth small but sharp. Skin silvery, and 

 spinous on the ventral edge of body and alone: lateral 

 line. Eye 3 in. in diameter. Lower line of body 

 straight. F. J. Cole. 



University College, Reading, August 2. 



