294 



NA TURE 



[January 29, 1903 



A reviewer usually likes to point out omissions, but the 

 only one as yet noticed is that of the very recent 

 experiences of Wilbur Wright and his brother. And 

 evidently there are two accounts of Degen's attempts, of 

 which the more improbable one is here given. According 

 to the other, his machine would not rise until he attached 

 it to a balloon. 



The illustrations are excellent, but it may be as well to 

 warn the reader that when he sees a picture of an 

 aeronaut sailing over houses, trees, mountains, rivers 

 and even pyramids in an extraordinary looking machine, 

 it is not to be supposed that the journey depicted was 

 ever performed, or even that the machine was necessarily 

 constructed in the forms shown. Readers of the 

 " Histoire des Ballons" will remember the fantastic 

 figures of flying men in that book and will not be sur- 

 prised to find a few of the types reproduced here, but 

 now that experiments have been successfully made in 

 directed navigation through the air, it would be well if 

 some indication could be given on illustrations in future 

 books showing at a glance whether the flight which they 

 depict is a real flight or a mere flight of the imagination. 



G. H. Bryan. 



TERRESTRIAL MAGNETISM. 



United States Magnetic Declination Tables and 

 Isotonic Charts for 1902. By L. A. Bauer. Pp. 405. 

 (Washington : Government Printing Office, 1902.) 



THE activity of the United States Coast and Geodetic 

 Survey Department in carrying out a magnetic 

 survey of the States and outlying territories has long 

 been a subject of interest to magneticians, and in this 

 book we have the first complete information on the results 

 of that survey up to January 1, 1902, as regards the one 

 element magnetic declination. 



Tables, giving every observation made, occupy 142 

 pages, including positions, date of observation, values 

 observed and values reduced to 1902, followed by the 

 name of the observer or authority. The succeeding 138 

 pages are devoted to descriptions of the magnetic 

 stations occupied by the Survey between 1S81 and July, 

 1902. 



The accompanying chart of " Lines of Equal Magnetic 

 Declination " is based on the results plotted at about 

 5000 points, embodying all the latest declination data 

 of known value. The lines are true isogonals, drawn 

 with considerable sinuosities, representing the results of 

 actual observation and showing disturbances from normal 

 values, but as these latter have not yet been calculated, 

 the amount of disturbance and the centres of disturbance 

 have not been ascertained. The chart for Alaska gives 

 normal lines of the magnetic declination calculated from 

 all available observations, there being too few of the 

 latter from which to draw true isogonals. 



A welcome addition to the tables and charts will be 

 found in the opening chapter under the heading 

 " Principal Facts relating to the Earth's Magnetism," 

 showing our present state of knowledge of terrestrial 

 magnetism and the vast field open to future observers 

 and students of that branch of science. 



NO. 1735, VOL - 6 /] 



In this chapter, the evolution of the compass is treated 

 boldly and agreeably with the evidence of the best 

 authorities, and one rather looks for the date and the 

 name of the first person who applied that very important 

 addition to the mariner's compass — its suspension in 

 gimbal rings. It is clear that the use of this suspension 

 was implied by Pedro de Medina in his "Arte de 

 Navigacion " of 1545, and was accurately described as 

 part of a compass by Martin Cortes in his " Arte de 

 Navigacion " of 1556, but they leave the inventor's name 

 in obscurity. 



Turning to the subject of Gilbert's work, " De Mag- 

 nete," the author remarks on the " intolerance and lack 

 of appreciation of the work of his predecessors" shown 

 by Gilbert. When, however, one reads the account given 

 by the latter of the mass of ignorance and superstition he 

 had to battle with and relinquish to "the moths and 

 worms" — such as the medicinal properties of the lode- 

 stone and its uses as a detector of immorality and many 

 other " vanities" — we can hardly wonder at their beget- 

 ting a spirit of intolerance in him. Even "theOnyon 

 and Garlick myth " which he so denounced was revived 

 in 1885 by an inventor who proposed the use of the juice 

 of the common Dutch red onion as a magnetic screen. 

 Possibly some readers of the present work will think the 

 author has not quite done full justice to Gilbert. 



On p. 6o, the authority of the late Prof. Eschenhagen 

 is given for the statement that the effects of earthquakes 

 on the magnetic needle are "entirely mechanical." As 

 the more recent investigations of Prof. Milne point to an 

 opposite conclusion, there is evidently room for further 

 inquiry as to how far the disturbances observed are due 

 to magnetic causes or not. 



In the article on magnetic observatories, some useful 

 details are given of the structure of the magnetic observ- 

 atory at Cheltenham, Maryland, where, although it is 

 built entirely above ground, the diurnal change of tem- 

 perature has been reduced to a few tenths of a degree, 

 and further reduction is looked for. 



In conclusion, it may be remarked that some of the 

 illustrations are taken from rare prints, and their repro- 

 duction cannot fail to be of great interest to many who 

 may not have the means of seeing the originals. Pleased 

 as the investigator may be with the valuable results con- 

 tained in this book, he will look forward with enhanced 

 interest to a similar publication relating to the magnetic 

 inclination and force, both of which have been so exten- 

 sively observed in the United States. 



OUR BOOK SHELF. 



Letters on Reasoning. By J. M. Robertson. Pp. xxviii 

 + 24S. .(London : Watts and Co., 1902.) 



THIS book is in the form of letters addressed to the 

 author's children, and is lucidly and fluently written. 

 Mr. Robertson's counsels upon the duty and importance 

 of clear thought and scrupulous candour in reasoning are 

 excellent, and it is to be hoped the children to whom the 

 letters are addressed will profit by them. It is a pity 

 Mr. Robertson does not always follow his own good 

 advice. In the constant polemic against theism, to 

 which he recurs in chapter after chapter, he often un- 

 consciously misrepresents the case against which he is 



