Oct 17, 1878] 



NATURE 



641 



every case the experiment consisted in a comparison of 

 the manuring effect of three parts of phosphoric acid in 

 an insoluble form, with a mixture containing one part of 

 soluble and one part of insoluble phosphoric acid. The 

 result was somewhat in favour of the latter mixture. It 

 Avill be seen at once that the experiment afforded no fair 

 comparison of the two forms of phosphate. Besides the 

 fatal error of mixing the soluble and insoluble phosphates 

 together, and comparing them in unequal quantities, 

 the amount applied to the land was far too large. 

 Let them drill with one set of turnips 2 or 3 cwts. of 

 superphosphate in which the whole of the phosphoric 

 acid is soluble, and apply to another plot the same 

 amount of phosphoric acid in the so-called insoluble form, 

 and the result of the comparison will be very different to 

 that at present shown. 



In speaking of the effect of nitrogenous manures the 

 report correctly states that they produce but little effect 

 on the turnip crop. The fact is that turnips have a 

 gfreater power than most farm crops of assimilating the 

 nitrogen of the soil, and being thus able to feed them- 

 selves stand in little need of artificial help. Where, how- 

 ever, the soil is in an exhausted condition, nitrogenous 

 manures will always produce a marked effect. 



The analyses of the turnips grown by the experi- 

 mental manures supply a variety of "new and unex- 

 pected information." Much of this is true in substance, 

 but is already well known to agricultural chemists. We 

 abstain from criticising, for we are sure the next report 

 will show a far better acquaintance with the chemistry 

 of the subject, and that the industry and zeal now dis- 

 played will finally issue in real additions to our know- 

 ledge of agricultural science. 



Eiiclid. Books I. and II. Edited by W. H. H. Hudson, 

 jM.A. Algebra. By the Same. (London ; The Society 

 for Promoting Christian Knowledge). 



The Euclid is founded on Simson's second edition 

 (1762). In addition to the text there are a few definitions 

 and some judicious explanatory notes. The Algebra (or 

 Primer as the author styles it) is divided into three parts, 

 Part I. Notation, Addition, and Subtraction; Part II. 

 Multiplication, Division, and Simple Equations ; Part 

 III. Measures and Multiples, Fractions, and Quadratic 

 Equations. The proof here given of -aX - b = ab, 

 due to Euler, appears to be quite sound. Mr. Hudson 

 states his belief that this proof was misunderstood by 

 Mr. Mill in his criticism ("Logic," vol. ii., ninth edition, 

 p. 408). This little work is an excellent one, and con- 

 tains a vast amount of good matter in a small compass. 

 Mr. Hudson has performed his task in no perfunctory 

 manner. Both books are brought out with a view to 

 teaching the subjects of which they treat as required by 

 the new code. They are very neatly printed and got up. 



LETTERS TO THE EDITOR 



\The Editor does 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. 

 No notice is taken 0/ anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com' 

 munications containing interesting aitd novel facts.'\ 



The Magnetic Storm of May 14, 1878 



In regard to the communication on the magnetic storm of 

 May 14, 1878, which appeared in Nature, vol. xviii. p. 617, 

 it may be interesting to add some particulars furnished by 

 examination of the magnetic photograplis of the Royal Obser- 

 vatory. 



For some days preceding May 14 the trace of the declination 

 magnet had been very quiet, exhibiting only the ordinary 

 diurnal change ; but on May 13, at i8h. 501., Greenwich 

 mean time, the character of the ciuve abruptly and distinctly 



changed, small and frequent oscillations commencing then to be 

 shown. At about 6h. on May 14 the north end of the needle 

 began to move gradually in an easterly direction, and at about 

 gh. had reached a position twenty-five minutes of arc east of its 

 usual position, the small oscillations still going on. No great 

 change then occurred until iih. 45m., when the north end of 

 the needle began to move sharply westward. At midnight it 

 had moved twenty minutoB westward, occup5nng then its nsual 

 position nearly ; almost immediately, however, it turned again 

 eastward, and at I2h. 40m. had moved twenty minutes in 

 that direction; after this time, with the exception of two 

 smaller bends, no other unusual motion occiu-red, and the 

 magnet gradually resumed its ordinary position. The small 

 oscillations first spoken of ceased at about the time of the 

 commencement of the first rapid motion, at iih. 4Sm. 



The commencement of the disturbance is not so distinctly per- 

 ceptible in the trace of the horizontal force magnet, but con- 

 tinued small oscillations occur through the evening of May 14. 

 At iih. 45m. the northerly force had (gradually since 6h.) de- 

 creased nearly o'oi part of the whole horizontal force ; it then 

 increased rapidly, and at midnight had about reached its usual 

 magnitude; by I2h. 40m. it had again considerably diminished 

 (but less than before), and after this time the magnet gradually 

 resumed its usual position. The small oscillations ceased about 

 midnight. 



The vertical force magnet trace shows a few very small oscil- 

 lations during the evening ; after 7h. the force decreased gradually 

 till midnight; at the latter time a sharper decrease occuried ; at 

 I2h. 30m. the force had altogether diminished by about 0*003 

 parts of the whole vertical force ; after this time the magnet, 

 rather rapidly at first, but afterwards more gradually, returned 

 to its ordinary position. 



The first start in the trace of the declination magnet, at i8h. 

 5m,, is most distinct ; the character of the trace definitely 

 changes at that time. If the commencement of disturbance is 

 as sharply indicated in the China, Melbourne, and Stonyhurst 

 registers, we shall have here a well-established instance of simul- 

 taneous, or nearly simultaneous, action, at widely-separated 

 parts of the earth's sm'face. The disturbance practically ceased 

 at Greenwich, May 14, i6h. It was comparatively large as 

 occurring in an otherwise quiet year. In years of activity these 

 motions of the magnets, in amount, are, on many days, much 

 exceeded. William Ellis 



Royal Observatory, Greenwich, October 12 



P.S. — Earth currents were active at Greenwich diuring the 

 whole period of the magnetic disturbance. 



Cyclones and the Winter Gales of Europe 



Mr. S. a. Hill, in Nature, vol. xviii. p. 617, compares 

 together the number of hours of high wind in the Bi^itish Isles 

 with the number of West Indian cyclones observed in each year 

 from 1869 to 1874. It may be interesting to add the result given by 

 the Royal Observatory register. The hourly values of velocity 

 in the years mentioned have not yet been tabulated, but adopting 

 for comparison the number of days on which the daily velocity- 

 exceeded 5C0 miles, we have counted up the number of ^uch 

 days in each year, which numbers, for more ready comparison 

 with those given in Nature, we have multiplied by a constant. 

 The comparison with the values previously printed in Nature 

 then stands as follows : — 



1869 1870 1871 1872 1873 1874 

 Cyclones (W. Indies) 07301? 



Hours of high wind ) ^.^ -_. -.» /-„- --. /r-c 

 (British Isles) ... 1 ^14 S7o 537 6,9 S7i 658 

 Days of high wind, 1 



Royal Observatory, \ 975 525 175 725 750 575 



X 25 ) 



William Ellis 

 Royal Observatory, Greenwich, October 12 



Height and Shape of Mount Hekla 



I NOTICE that there is a mistake in regard to the height of 

 Hekla in the map vhich accompanies my account of the 

 eruption of February 27, 1878, for which I fear I am alone 

 responsible. It is there stated to be 4,950 feet. The real 

 height is 4,961 Danish feet = 5,108 English feet. The height 

 has been frequently mLsstated, Sometimes it is asserted to be 



