io6 



NA rURE 



[December i, i! 



the apparatus consist entiiely of rigid parts, as in optical experi- 

 ments, there is no better way of ensuring steadiness than by 

 placing the optic bench on a heavy table whose legs rest on four 

 blocks of india-rubber. 



Dr. H. F. Moore, of the United States Fish Commission, is 

 reported by Scieiue to have been making a careful examination 

 of the physical conditions of Great Salt Lake, with a view to 

 determine its adaptability to oysters and other salt-water and 

 brackish-water animals. While it is known that the salinity of 

 the open lake is so great as to preclude the possibility of the 

 acclimatisation of useful marine animals, it has been suggested 

 that there are certain bays or arms of the lake, in which rivers 

 discharge, where the density is lowered to a point somewhat less 

 than that of ocean water, and where it may be possible for 

 clams, oysters, crabs, terrapins and such animals to survive and 

 multiply. Dr. Moore has not completed his inquiries, but it 

 may be said that the outlook for an augmentation of the aquatic 

 food resources of this region is not very promising, the amount 

 •of fresh water entering the lake being subject to great variation, 

 and the existence of a naturaJ food supply for the introduced 

 species being uncertain. 



Owing to the thoroughness of the investigations made on the 

 Challenger and other deep-sea explorations, our knowledge of 

 the deposits of ocean depths is, if not more extensive, more 

 coherent and better generalised than that of the more complex 

 and changeable deposits in the shallower coastal waters. Great 

 interest therefore attaches to the systematic exploration of the 

 Irish Sea bottom, now being carried on by the Liverpool 

 Marine Biological Committee, of which an instalment appears 

 •n the recent number of the Proceedings of the Liverpool 

 Oeological Society. Messrs. Herdman and Lomas describe and 

 classify forty-four dredged samples, and discuss some of the 

 general questions raised. Among other things the rottenness of 

 many aragonite shells as contrasted with calcite shells, and the 

 general occurrence of organic remains in a drifted condition, 

 rather than in situ, are of special geological interest. The 

 authors remark that "a place may be swarming with life and 

 yet leave no trace of anything capable of being preserved in the 

 fossil state, whereas in other places, barren of living things, 

 banks of drifted and dead shells may be formed, and remain as 

 a permanent deposit on the ocean floor." 



A.N essay on certain eruptive rocks from the Transvaal, and on 

 other South African rocks, forms the inaugural dissertation sub- 

 mitted by Mr. J. \. Leo Henderson to the University of Leipzig, 

 in order to obtain the degree of Doctor of Philosophy. It is 

 published by Dulau and Co, The rocks to which attention is 

 specially directed are the olivine-free Norites, Gabbros and 

 Pyroxenites of the Transvaal ; and it is remarked that the 

 Norites of the Zwaartkoppies range (hitherto termed Gabbros) 

 have mutually intergrown or interlocked rhombic and mono- 

 clinic pyroxenes. Attention is also drawn to the occurrence of 

 Anorthoclase rocks of the holocrystalline as well as porphyritic 

 facies. These latter arc free from quartz, and therefore cor- 

 respond to the Syenites, being evidently the link between the 

 Syenitic and Clranilic rocks on the one hand, and the Diorites 

 and Diabases on the other. For these holocrystalline and 

 porphyritic types of rock respectively, the author suggests the 

 names of " Hatherlite " and " Pilandite," from the localities 

 (Ilatherley and Pilandsberge) where they have been met with. 

 Fcirster's name of " Pantellerite " applies to the volcanic 

 equivalents of these rocks. The essay is illustrated by five 

 plates. 



The old maxim of "If at first you don't succeed, try, try 



try again," is a very good one to keep in mind when endeavour 



ing even to produce anything good in the photographic line, 



Success has at la.st rewarded the efforts of Mr. J. K. Johnson, 



NO. 15 l8, VOL. 59] 



who has been experimenting since the year 18S6 in the manu- 

 facture of half-tone cross-line screens for use in the production 

 of process-engravings. Many of us admire the really beautiful 

 reproductions that are of every-day occurrence in our illus- 

 trated publications ; but how few are there who inquire into the 

 processes by which such illustrations are made possible. If 

 our readers are interested in this kind of work, let them take 

 an illustration by one of these processes, and apply to it a small 

 magnifying glass and examine the texture, so to speak, of the 

 detail. Several excellent illustrations are reproduced in The 

 Process Photogram for November, and are accompanied by the 

 first of a series of articles which describe the British half-tone 

 screen: the word " British " is here used because, until quite 

 recently, the whole of the manufacture of these screens was in 

 the hands of Mr. Max Levy, of Philadelphia. The screens 

 which Mr. Johnston has succeeded in making indicate an im- 

 portant departure in British manufacture, and they are capable 

 of doing very fine work. A great amount of money has already 

 been unsuccessfully spent by British, German and French 

 machine-rulers to produce satisfactory half-tone screens, and it 

 is satisfactory to be able to record the fact that a British firm I 

 has thoroughly solved the problem. The above-mentioned 

 article, and those that will follow it, give some technical par- 

 ticulars of these new screens, and will be found very interest- 

 ing. Incidentally we may mention that the Phologram for 

 November is full of interesting matter and the usual well- 

 reproduced illustrations. 



An illustrated paper on the ruins of .\kichmook, Yucatan, 

 prepared by Mr. E. H. Thompson, has been published by the 

 Field Columbian Museum, under the auspices of which the 

 archaeological investigations described were carried on. Exca- 

 vations were made at many points, walls were uncovered and 

 traced, cisterns were cleaned out, graves were examined, and 

 many objects of art were procured. Pottery and flaked stone 

 implements were plentiful, but polished implements and 

 specimens of sculpture were exceedingly raie. .\Ir. Thompson 

 remarks that at .\kichmook and elsewhere in Yucatan he has 

 never found a single obsidian implement, except slender blades 

 that probably served as knife blades. At Xkichmook he found 

 more plentiful traces of the ancient fabrication of flint implements 

 than in any other group of ruins. With the exception of a celt 

 fragment made of nephrite, not a single polished stone imple- 

 ment was found. 



A catai.oi'.i:f. of more than two hundred pages, containing 

 particulars and prices of books and papers offered for sale, 

 has just been issued by Messrs. Dulau and Co. 



A I'Oi'ULAR account of Etna and some of its eruptions, illus- 

 trated by several reproductions of photographs, and a contour 

 map of the central crater, is contained in a brochure by Prof. 

 Albin Belar, just published at Laibach. The description has 

 been reprinted from the Laihcuher Zeitung. 



Dr. R. \'. Wki rsiKiN has reprinted, from the Transactions 

 of the (German) Bohemian Association for Natural Science and 

 Medicine, an interesting paper on the means of protection of the 

 flowers of geophilous pl.ints, i.e. those in which the flowering 

 branches are formed beneath the surface of the soil. 



The first of a series of papers on new or imperfectly known 

 species of earthworms collected from various parts of the 

 Japanese empire is contributed to Annolationes Zoologicae 

 Japonenses (October 10) by Prof. Seitaro Goto and Mr. 

 Shinkichi Ilaiai. 



Messrs. Sampson Low, Marston, & Co. have published 

 an English edition of the very interesting " New Astronomy," 

 by Prof. David P. Todd, recently reviewed in Nature 



