Feb. 3, 1881] 



NA JURE 



3^0 



with great precision. The charts accompanying Sabine's 

 "Contributions to Terrestrial Magnetism," No. ix. {Phil. 

 Trans. 1849), were among the earliest on which the data 

 whence the curves were drawn are recorded, although it 

 may be observed that even a portion of the observations 

 made at sea and utilised in these charts had no correc- 

 tions applied to them for the effects of the ship's iron. 



Considering the local magnetic disturbance found to 

 exist on land in many regions and the large area of water- 

 covered portions of the globe, observations made at sea, 

 when systematically carried out and corrected for local 

 attraction in the ship, have become an important factor 

 in ascertaining the magnetic variation for the use of 

 navigators at any given epoch. 



Evans's Variation chart for the epoch 1S58, embracing 

 the navigable parts of the world, and in which the whole 

 of the observations made at sea were corrected for the 

 effects of the ship's iron, was published by the .Admiralty. 

 A further advance on Variation charts of an earlier date 

 was the addition to this of a map showing the amount of 

 annual change of the variation as determined at several 

 localities, enabling reductions for the succeeding ten 

 years to be made with a reasonable approach to the 

 truth. 



The increase of iron-built and composite vessels in late 

 years has rendered a reliable Variation chart a necessary 

 adjunct to navigation. This object appears to have been 

 kept steadily in view by the Hydrographic Department of 

 the Admiralty, for, in 1871, a new edition of the " Varia- 

 tion Chart of the World," reduced to that epoch (with 

 polar charts added) was published in continuation of the 

 chart for 1858. This chart was the result of the joint 

 labours of Capt. Evans and a member of the compass 

 department, Navigating-Lieut. Creak, R.N. 



We have now to notice the more recent publications of 

 these contributions to terrestrial magnetism. A chart of 

 the curves for 1880, in continuation of those for the 

 epochs 1858 and 1871, by Staff-Commander Creak, has 

 been published by the Admiralty. In its construction 

 the observations made during the voyage of H.M.S. 

 Challenger (1872-76) have been introduced, and amongst 

 results from other sources, specially those taken from 

 Mr. A. Schott's papers on the secular change of the 

 variation published as Appendix No. 8 to the U.S. Coast 

 Survey Report for 1S74, and also as a preliminary publi- 

 cation to the Report for 1879 ; Ur. Thorpe's observations 

 in the United States, made about the 40th parallel of lati- 

 tude, and results from the maps of the excellent magnetic 

 survey of a large portion of the Eastern Archipelago in 

 1874-77, made by Ur. Rijckevorsel, have also been 

 included. 



As confined to special portions of the world a map of 

 the United States for the epoch 1S75, constructed by Mr. 

 J. E. Hilgard, Assistant U.S. coast and geodetic surveys, 

 published in the America}!, yoiirnal of Science for March, 

 1880, and illustrating an article on the subject of magnetic 

 variation or declination, is of a high order of excellence. 



In this map the curves, which show several flexures 

 strictly pourtraying results arising from local disturbance, 

 have been drawn for every degree of [equal] variation. 

 The results are from observations made during the pro- 

 gress of the U.S. Coast Survey up to 1877, also from 

 about 200 observations made in the interior of the country 

 under the direction of Mr. Hilgard, to which were added 

 every available observation from the land and boundary 

 surveys, as well as those of private observers. Many of 

 these results having been obtained at different periods of 

 time, have been reduced to the given epoch by means 

 of Mr. A. Schott's paper on Secular Change before 

 referred to. 



Although in maps and charts covering large geogra- 

 phical areas the variation lines for the land poitions are 

 generally drawn in regular curves (and so far deviating 

 from strict accuracy), whilst those for the larger sea areas 



are necessarily so done, still in delineating the magnetic 

 features of a portion of a continent the system followed 

 by Mr. Hilgard, as also by Lament in his European 

 surveys between 1850 and i860, commends itself for 

 accuracy. 



The late Prof A. D. Bache, who took a personal 

 interest in the study of terrestrial magnetism, bequeathed 

 a fund for scientific research. The expenses of obtaining 

 the 200 observations in the interior of the United States 

 before mentioned, were defrayed by a grant from this 

 fund. 



THE ZOOLOGICAL STATION AT NAPLES 

 " AIT'HAT ?> a zoological station?" is a question we 

 '' * have often heard asked when Dr. Dohrn's insti- 

 tution at Naples is under discussion. A " zoological 

 station " (according to Dr. Dohrn), we may reply, is a 

 kind of zoological garden for marine animals, or what is 

 commonly called an " aquarium," only that, contrary to 

 the usual practice at Brighton, Westminster, and else- 

 where, the scientific element of the establishment is 

 mostly cultivated instead of the popular branch. Such 

 at least is the case under Dr. Dohrn's system, and also, we 

 believe, in other zoological stations that have been formed 

 after his example. 



It must be recollected that the lower forms of organic 

 life, to the study of which zoological stations, as thus 

 described, are mainly devoted, are much more numerous 

 than the vertebrata, and much less understood. Even in 

 our own seas a vast amount remains to be done before 

 our knowledge of the thousands of marine organisms 

 which populate our waters and shores can be deemed to 

 be anything like complete. Still more is this the case in 

 the Mediterranean, where under a bright sky and burning 

 sun the clear waters teem with animal life in all its 

 varieties. It was no doubt the weH-known productive- 

 ness of the coast of Naples and the facilities offered for 

 dredging in its land-locked Bay that induced Dr. Dohrn 

 to fix his "Zoological Station" in this quarter instead of 

 planting it on the shores of his Fatherland. 



After several years of incessant labour Dr. Dohrn has 

 got his establishment into excellent working order, and, 

 as will be seen by our advertisement pages, promises us 

 after so much cultivation a rich and abundant harvest. 

 The proper subject to take up when the publication of 

 results was determined upon was obviously the Biology 

 of the Bay of Naples. Great difficulties however beset 

 the advance of this project. As regards the Fishes, the 

 more highly-organised Crustaceans, the Mollusca, and 

 some of the Ccclenterata and Echinodermata, it appeared 

 possible for the students at the Zoological Station to avail 

 themselves largely of the results arrived at by former 

 workers. But when they proceeded to examine into the 

 scattered literature in which the innumerable armies of 

 Lower Crustaceans, Annelids, Nemertians, Planarians, 

 Nematodes, and such-like creatures are described, the 

 case was very different. The ancient naturalists have 

 mostly characterised their species in these groups in such 

 vague diagnoses that it is impossible to identify them. 

 Under such circumstances the students of the higher 

 animals are accustomed to resort to the type-specimens 

 whence the descriptions M-ere taken in order to see what 

 the authors really intended. But the impossibility of 

 preserving many of the lower animals cuts this re- 

 source away from the marine zoologists, who have con- 

 sequently contented themselves in some instances with 

 referring their specimens to species never sufficiently 

 described, in other cases with describing them as new. 

 Hence has arisen a mass of confusion which can be only 

 regarded as parallel to what existed among the more 

 highly-organised animals in the ante-Linnean period. The 

 transformations undergone by many of the lower marine 

 animals and the extraordinary sexual differences add 



