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LXXVII. Memoir on the Diminution of the Olliquity of the. 

 Ecliptic, as resulting from ancient Observations. By 

 M. Laplace. Translated from the " Connoissance 

 des Terns for 181 1" &y Thomas Firminger, Esq. 



To Mr. TillocL 



Sir, J. he variation of the obliquity of the ecliptic having 

 been a phenomenon in astronomy of a nature to engage the 

 most lively interest of those who have made this sublime 

 and useful science the subject of their study, and as its in- 

 vestigation has never been fully developed till the appearance 

 of that profound work the Mecanique Celeste of M. Laplace, 

 I have no doubt the following comparison of ancient ob- 

 servations with the deductions derived from his formula 

 will be highly interesting to many of your readers. The 

 article is taken from the Connoissance des Terns for the year 

 1811; and the only apology offered for its translation is 

 the extreme scarcity of that work in this country : it was 

 drawn up by the profound mathematician and philosopher 

 above mentioned, with a view to compare his deductions 

 with the actual state of the system at an interval of time as 

 great as observations of sufficient accuracy would admit; 

 and the coincidence, taking into consideration the imperfect 

 state of science in those ages, is remarkably striking. It 

 pres'ents to us not only one of the most undeniable proofs 

 of the Newtonian principle of gravitation, a fabric on which 

 the whole of the Mecanique Celeste is founded, but furnishes 

 the historian with facts which give additional credit to the 

 faithfulness of the narration. On this as well as on other 

 occasions we have a right to form our opinion from analogy. 

 We see the recorded observations agree, as nearly as the state 

 of science in those days will admit, with what theory has 

 assigned to them; and as they do not make a separate his- 

 tory of themselves, but are coupled with the history of 

 the times in which they were made, the known truth of the 

 one gives a satisfaction to the mind in appreciating the value 

 to be affixed to the other. If we look to the account given 

 in the Lunar Tables published by the Board of Longitude 

 in France, we shall find those tables were compiled princi- 

 pally from the astronomical observations made in the Royal 

 Observatory at Greenwich ; and not only the epocha, but the 

 present state of diminution in the obliquity of the ecliptic 

 has been in a great measure determined from them: we 

 shall not, therefore, be surprised to fiud, hereafter, a nearer 



coin- 



