April 13, 1893] 



NATURE 



555 



MAGNETIC OBSERVATIONS IN THE 

 NORTH SEA. 



Magnetische Beobachtungen auf der Nordsee angestellt 

 indenjahren 1884 (J/j 1886, 1890 und 1891. Von A. 

 Schiick. (Hamburg: Selbstverlag des Verfassers, 

 1893) 



THE extended and valuable magnetic surveys — 

 notably those of Riicker and Thorpe in England, 

 and of Moureaux in France — which have been made 

 during the last ten or fifteen years, have provided 

 magneticians with considerable information as to the 

 conditions of the earth's magnetism in the countries 

 bordering on the North Sea. From such data, there 

 should be no difficulty in calculating normal curves of 

 the three magnetic elements for the comparatively small 

 intervening region covered by that sea. 



The surveys on land have, moreover, shown that there 

 are several regions of local magnetic disturbance, and 

 therefore the chief interest of a magnetic survey of the 

 North Sea, would lie in the discovery from observation on 

 board ship, whether local magnetic disturbance existed 

 in the land under the sea. The settlement of such a 

 point would be a valuable contribution to our knowledge 

 of terrestrial magnetism, and certainly if large dis- 

 turbance were observed in any locality, of great 

 practical importance to navigation. 



Captain A. Schiick has, for some years, past been 

 making observations of the three magnetic elements with 

 a special set of instruments well designed for observa- 

 tions at sea. Great pains have been taken by him to 

 eliminate all sources of instrumental error, and he 

 selected those wooden ships which appeared to him so 

 far free from iron in their construction, that his magnetic 

 instruments when mounted on board would be undis- 

 turbed. The results of his four years' work are given in 

 the text with full descriptions, and illustrated by draw- 

 ings of the instruments, as well as a chart of curves of 

 equal value for each magnetic element. 



The execution of these charts leaves much to be 

 desired, for the figures on the land are in many places so 

 crowded together as to be almost illegible, and it would 

 have been much more to the purpose, if the lines of equal 

 values had been at once taken from the published maps 

 of the several observers, whose work the author fully 

 acknowledges, instead of crowding together the data 

 upon which their lines are based. 



Again, the curves for those regions covered by the sea 

 are in places so abnormal that they invite inquiry as to 

 the accuracy of the small number of observations upon 

 which they in many parts depend. 



Although the author gives general assurances as to the 

 selected ships being free from any source of magnetic dis- 

 turbance, there are really no results recorded, to show 

 that the observations at sea were really free from the 

 effectsof iron in the several vessels on board which the 

 magnetic instruments were used. Long experience shows, 

 that unless specially built, no wood-built ship is so far 

 free from iron that its action can be neglected, especially 

 when minutes of arc in an observation are of importance. 



If observations at sea over so small an area as the 

 North Sea, and the channels south and west of Great 

 Britain, are to effectually supplement those extensive 

 NO. 1224, VOL. 47] 



magnetic surveys made on the countries adjacent thereto, 

 they must be stripped of every source of error. It does 

 not appear that the observations recorded in this work 

 are of the exact order suitable to modern requirements, 

 however useful they might have been many years ago. 



A work like that undertaken by the author, requires a 

 specially-constructed vessel, devoted for the time to 

 magnetic observations and other subjects of scientific 

 inquiry. His objects were evidently delayed in execution 

 by insufficient means to a satisfactory end. 



MANUAL OF DAIRY WORK. 

 Manual of Dairy Work. By James Muir, M.RA.C., 

 Professor of Agriculture in the Yorkshire College, 

 Leeds. 93 pp. (London: Macmillan and Co., 1893.) 



THIS small primer on dairy work is in several respects 

 a contrast to some of the books and pamphlets 

 relating to dairy matters which have appeared within the 

 last two or three years. Many of these have had too many 

 points in common with a dairy utensil manufacturer's 

 catalogue, and the information they contain has not always 

 been either condensed or trustworthy. It is therefore 

 a pleasure to take up Prof. Muir's little manual, which 

 gives in small compass a great deal of information likely 

 to be of value to every one interested in the production 

 and use of milk. Apparently the book is intended for 

 those who, having practical knowledge of the manage- 

 ment of milk and its products, desire further knowledge 

 of the principles upon which their practice is ba=;ed, 

 together with hints as to the best means of utilising their 

 commodity according to the demands of their own 

 particular market. 



The information given is in most cases well up to date, 

 but at the same time the discussion of obscure matters 

 connected with the bacteriology of milk is carefully 

 avoided. This is the more to be commended because 

 every teacher of agriculture must know that looseness in 

 describing the work of micro-organisms producing decay, 

 or nitrification, or fixation of free nitrogen, has in many 

 cases caused utter confusion in the minds of students ; 

 and more especially harmful is the imagination sometimes 

 exercised by reporters and writers for the agricultural press. 

 It is difficult to estimate the importance of Bacteriology 

 in its relations to Agriculture and to Dairying, but in all 

 discussion of the subject it is well to keep to ascertained 

 and confirmed fact. 



Prof. Muir's book is divided into ten chapters, 

 the first of which deals with the formation and 

 composition of milk. The description of the for- 

 mation of milk in the udder is a trifle loose, the entire 

 process being described as a casting off and breaking 

 down of the cells which line the alveoli of the mammary 

 glands. Milk is no doubt largely produced in this way, 

 and especially must this be the case with colostrum when 

 the glands commence or resume their activity ; but it is 

 more than probable that afterwards the milk is to some 

 extent elaborated from the blood through the activity of 

 the cells without so much actual shedding of the cell s 

 taking place. The great difference in composition 

 between colostrum and normal milk shows that this 

 latter process must be an important one. 



