124 



NATURE 



\yune 14, 1877 



ments, which really may be the cause. But, probably, if in 

 future times it be found by improved methods and instruments 

 that the law does not hold, it would be advantageous to pro- 

 claim by definition the conservation of energy and to deduce 

 from it the measurement of time. Then we should have the 

 analogon of the absolute scale of temperature of Thomson. 



If any one after the perusal of this article asserts that my 

 views are at variance with the historical development of science, 

 I answer that often in the reasoning of man there are gaps, 

 which by contemporaries are not perceived ; but that we must 

 try to find them out and to fill them. 



I hope my readers will not be too much annoyed by the de- 

 fective manner in which I may have expressed myself in English ; 

 it is always difficult to make use of a foreign language. 



Before closing I am bound to state that I have particularly 

 mentioned the assertions of Sir W. Thomson, Prof. Tait, and 

 Prof. Clerk Maxwell, because in their works I found most 

 emphatically stated what in my opinion is erroneous. These 

 eminent men stand so high that it is unnecessary for me to ex- 

 press my profound respect for them. V. A. Julius 



Roermond, Holland 



OUR ASTRONOMICAL COLUMN 



The D'Angos Comet of 1784. — Encke's investigation 

 relating to this reported comet appears in Zach's Corre- 

 sp07idance Astroiioinique, as an " Imposture Astronomique 

 grossi^re du Chevalier D'Angos, ddvoilde par J. F. Encke, 

 k Gotha." Olbers, in a letter addressed to him, had, as 

 already stated, asked his attention to the subject, saying, 

 " I would invite you to the examination of a doubtful 

 comet of which the result will be either the knowledge of 

 the yet unknown orbit of a very remarkable comet, or 

 the discovery of a most shameful imposture," and adding 

 particulars to which allusion is made in our previous 

 note. 



Encke remarks at the outset that, contrary to all gene- 

 ral usage amongst astronomers, D'Angos had given 

 the Malta observations with mean times for Paris, and 

 the comet's positions expressed in longitudes and lati- 

 tudes, which confirmed the suspicion that he had com- 

 puted from the elements of an imaginary orbit and had 

 not taken the trouble to convert the results into right 

 ascensions and declinations, in which astronomers are 

 accustomed to present them. If it is demonstrable that 

 according to the observations (at least without supposing 

 them erroneous to the amount of many minutes) the 

 comet could only have moved in a very improbable orbit, 

 in fact almost as a satellite of the earth and at a distance 

 less than that of the moon, and if further it can be 

 shown that by a very simple error of calculation D'Angos 

 was misled in deducmg the places of the comet from the 

 imaginary elements, then, Encke urged, there remains no 

 longer the smallest doubt that he had invented all these 

 observations. Making use of the positions given for April 

 15, 22, and 29, Encke assuming arbitrarily a value of the 

 comet's curtate distance from the earth at the first date, 

 finds the corresponding value for the same at the third 

 date in order to represent precisely the longitude on 

 April 22, and compares with the corresponding latitude. 

 Thus if the curtate distance on April 22 be taken as 0'42 

 (we somewhat contract Encke's figures) the third distance 

 IS 055, the error on the middle latitude, — 16', and the 

 resultmg conic section is a hyperbola ; the same form of 

 orbit is deduced when the comet's distance on April 22 is 

 diminished tn 0^25. If this distance be further diminished 

 to o'i46, the orbit becomes an ellipse, but the error on 

 the middle latitude is still — i2''8, and it was found neces- 

 sary to reduce the curtate distance to 000126 in order to 

 represent this latitude with no greater error than — 2''5 ; 

 the resulting orbit being also an ellipse. Taking the solar 

 parallax at 8"86, this distance corresponds to 116,000 

 miles, or about half the moon's distance from the earth, 

 and under the condition named above, on April 29 it 

 ■would still be less than 160,000 miles. Thus Encke found 



it was necessary to assume the comet's distance from the 

 earth, almost incredibly small if the errors of calculation 

 are to be brought within the limit assigned by D'Angos 

 to the differences between the places computed from his 

 elements and his observations, or about l|' ; and, he con- 

 tinues, a celestial body under such circumstances remain- 

 ing for so long a time in immediate proximity to the earth, 

 would assuredly have been retained within its sphere of 

 activity, and D'Angos if he were the first would certainly 

 not have been the only observer of this second moon. 

 Rejecting then as beyond probability the conclusions 

 necessarily drawn from an investigation in the manner 

 here briefly described, Encke proceeded to examine the 

 calculation of geocentric longitudes and latitudes of the 

 comet from the elements assigned by D'Angos. 



Taking for example the observation of April 15, the 

 logarithm of the radius- vector calculated from the orbit of 

 D'Angos is found to be 9'82o8333, and continuing the 

 computation the resulting position diff'ers from the obser- 

 vation 47° in longitude and 15° in latitude, but supposing 

 that by an error of the pen D'Angos had used a log. 

 radius-vector ten times greater, or o'82o8333, with the 

 same heliocentric longitude and latitude, the errors are 

 reduced to 56 seconds and 34 seconds respectively, and 

 making the same change in the log. radii-vectores at the 

 other dates of observation, Encke arrived at the extra- 

 ordinary result that the whole of the reputedly-observed 

 places were represented within about the limit of error 

 mentioned by D'Angos, and he insisted that with such 

 proof there could be no possible doubt that the observa- 

 tions and the orbit of the comet, " ne soient enti^rement 

 fausies et controuvdes, et que par consequent il faut les 

 rayer de tous nos catalogues des cometes, comme un astre 

 chimerique qui n'a jamais existd ;" while at the same time 

 he acknowledged himself ready to do justice to the accused 

 and to make the most ample satisfaction if he could be 

 opposed by arguments as strong and apparently con- 

 clusive as those upon which he had founded an adverse 

 verdict. 



The Total Solar Eclipse, 1889, December 22. — In 

 continuation of notices of future total eclipses of the sun 

 which have appeared in this column, the elements of the 

 eclipse of 18S9, December 22, are subjoined : — 



G.M.T. of Conjunction in R.A. Dec. 22, at oh. 24m. 50s. 



The central and total eclipse commences in long. 

 78° 52' VV., lat. 15° 22' N., and ends in long. 60° 55' E. and 

 lat. 6° 53' N., and it occurs with the sun on the meridian 

 in long. 6° 27' W., lat. 11° 5' S. 



At a point on the coast of Africa in 10" 6' S. lat., totality 

 commences at 2h. 8m. 55s. local time, and continues 

 3m. 34s. At Bridgetown, Barbadoes, totality begins at 

 6h. 47m. 6s. A.M. local time, and continues im. 48s., but 

 the sun's altitude is only 6^. The following are points 

 upon the central line, which will show that with a fair 

 duration where the sun is near the meridian, the course 

 of the eclipse is not a favourable one for observation :— 



Long. 



5*9 22 W. 

 47 39 

 32 28 W. 



Lat. 



13 30 N. 

 7 37 N. 

 023 S. 



Long. 



