104 



NATURE 



[November 29, 1894 



behoves me to confine my own remarks to this matter. In 

 order that my explanations may be understood, the table 

 previously given is here reproduced. 



This table is in every respect the same as originally given 

 with the exception of the v.alue for 1700, the erroneous value of 

 1 1' 5 S. having been given instead of 2' S. Owing to my sojourn 

 in Europe being but a temporary one, I have not with me all 

 my data, and so cannot ascertain definitely how this error crept 

 into my table. My original scaling was probably 15 S., which 

 by a copying blunder may have been converted into 1 1 -5. 

 This, however, I cannot control now. It would have been a 

 most natural inference on Mr. Wilde's part if he had ascribed 

 '.his to the " printer's devil," all the more so as no use what- 

 ever was made in the text of my communication with this 

 value. On account of so apparent an error he casts a slur upon 

 my trustworthiness in general in regard to terrestrial magnetic 

 matters. Such a poor method of argument reveals the weak- 

 ness of his position. 



Furthermore, with reference to this table, Mr. Wilde says : 

 " I regret to observe that L. h. Bauer, in his intolerance of the 

 magnetarium results, has inserted in his table guesses of his own 

 for observations, which are very wide of the truth." I can 

 find no excuse whatever for this statement. Mr. Wilde has 

 acknowledged that he possesses a copy of Hansteen's " Mag- 

 netisms der Erde." Let him turn to Tafel II. : " Neigung der 

 Magnetnadel," p. 36, and he will find the following observa- 

 tions given for St. Helena : — 



Position assigned by Hansteen: latitude 15° 55' S., longi- 

 tude II' 52' E. of Ferro, or 354' 12' E. of Greenwich. By in- 

 specting the table given above it will be seen that these form 

 Observations Nos. 2, 3, and 4. Xo. 5, as slated, is taken from 

 Hansteen's Chart for 1780. Mr. Wilde does not appear to 

 question this value, nor the remaining ones, which can be 

 easily found in Sabine's " Contributions to Terrestrial Mag- 

 netism." He will, furthermore, find thai Hansteen had so much 

 faith in the early observations, which Mr. Wilde insinuates 

 are unirustworlhy, that in 1857 he made use of all the observa- 

 tions known up to that time, viz. Nos. 2, 3, 4, 6, 7, 8, and 9, 

 for the establishment of a periodic formula representing the 

 secular variation of the inclination during this epoch. These 

 investigations of Hansteen's can be found in " Den magnctiske 

 Inclinations Korandringcr i den nordlige og sydlige Halvkugle 

 af Christopher Hansteen," Copenhagen, 1857, -4'. Hanslccn, 

 by a least square adjustment of the observations named, derived 

 the following interpolation formula : — 



1= - i3'58-455 - 5'-44405(/- iSoo) -o''ooioi3 (/- 1800)'. 



I denotes the inclination at the time /, south inclination 

 being reckoned as minus. This formula at the utmost should 

 not be used more than ten years prior to 1754, nor ten years 

 later than 1S46. The following table shows how the values 

 computed with this formula agree with observation. 



NO. 1309. VOL. 51] 



Date. 



1754-28 

 1771-58 

 '775'38 

 1 824 96 

 1S4010 



' 842-35 

 1846-79 



Observed 

 incUnaiion. 



From this comparison it will be seen that the formula re- 

 presents the observations fairly well. Let us compute then 

 with it what the inclination would be in 1747. We obtain 

 - 9°'2. Now Mr. Wilde's magnetarium has given us for this date 

 ihe value 00. Hence there is an oulstanding difierence of 

 about 9', which he has made no attempt to explain other- 

 wise than by insinuating that I have put "guesses" in my 

 table, or that the observations are unirustworlhy. The burden of 

 the proof that the observations are not trustworthy, rests with Mr. 

 Wilde. Anyone, who has made any endeavour to familiarise 

 himself with the literature of the subject of terrestrial mag- 

 netism, will know that it is an old story for theorists to charac- 

 terise observations as doubtful if they do not happen to agree 

 with their theory. I am willing to admit that the early inclina- 

 tions in such a locally disturbed region as St. Helena, perhaps, 

 cannot be depended upon nearer than to 2' or 3° ; but, if 

 Mr. Wilde will pardon my scepticism, 1 do not believe that 

 it is possible for him to reproduce .\ny inclination with his 

 magnetarium that can be relied upon even to this extent. 

 Hence, it is fair for me to compare the magnetarium results 

 with that of observations (so long as the latter have not been 

 overthrown) without consideration of the probable error of 

 either result. 



Mr. Wilde appears to have thought his position proven 

 when he found that I made an error wilh respect to my first 

 value. But even wiih the value as given by him, the outstand- 

 ing difference is 5°-6°, with which he. appears perfectly 

 satisfied. If he will permit me a probable error as large as he 

 permits himself in the establishment of his theory wilh his 

 magnetarium, I can supply him with a dozen periods that will 

 satisfy observations as well as his magnetarium. I would like 

 to refer him to a recent attempt by Dr. F'clgentraeger, who 

 endeavours to prove the universality of the secular period by 

 establishing periodic formuire upon the b.asis of most carefully 

 collected material. He deduces a period of 477 years — instead of 

 Mr. Wilde's 960— upon the basis of the declination observations 

 made at London 15S0-18S2, and Paris 1541-1890.' Adopting 

 this period he found that he could represent exceedingly well 

 the observations made at London, Paris, Rome, Clausthal, 

 Chambersburg (U.S.A.), Rio de Janeiro, Cape of (lood Hope, 

 and Cape Comorin. Here we have a more extensive comparison 

 than .Mr. Wilde has given us, and we find a better agreement 

 with observations with a period one-half of his! In this brief 

 communication I cannot set forth my o«n position with respect 

 to the secular-variation period. I hope to present Mr. Wilde 

 with a copy of my investigations some time in December. 



With respect to my opinion of the magnetarium in particular, 

 I may say that my criticisms m.ide thus far have applied solely 

 to the theory as evolved from the magnetarium results, and do 

 not touch the magnetarium as a valuable instrument of research. 

 Indeed, I think much good can be accomplished with it. Mr. 

 Wilde has m.ade a most laudable attempt to reproduce mechani- 

 cally the complex phenomena of terrestrial magnetism, and if 

 the achievements with his ingenious mechanism had not received 

 Ihe publicity they did, or had been propeilv iiilerpreted, my 

 criticisms would never have been made. That he has not 

 succeeded in giving us a better representation is no fault of 

 his, but owing to the complexity of Ihe phenomena. 



The fact that Mr. Wilde has succeeded, by an arbitrary dis- 

 tribution of magnetic mailer in his m.agnetaiium, in representing 

 the Jistriliulion of terrestrial m.agnetism for Ihe year 1880 

 apparently so well, is no proof of his secular-variation theory or 

 his period, which plays no part in determining the distribution. 

 Nor is the fact that wilh hii distribution of magnetic matter he 

 gets a good representation a proof that that is the actual distri- 



' Dr. W, K<:'KenIr.ieger : Die lungtle nachwciobarc Siiciil.irc Pcrinde der 

 erdm.-i(ineliichen Elenienie. 'Icil i: Deklinalion. Iiiailg. Diss. Universiut 

 zu li'-ltingcn, G"ttingen, \%i, Buchdru-.Ic'rci vnn Lou-s Hofer. 



