316 



with problems of perturbation, they are applied, in this essay, first, 

 to a very simple example, suggested by the motions of projectiles, 

 the parabolic path being treated as the undisturbed; and secondly, to 

 the problem of determining the motions of a ternary or multiple 

 system, with any laws of attraction or repulsion, and with one pre- 

 dominant mass. This latter problem, which was touched upon in the 

 former essay, is here resumed in a new manner, by forming and in- 

 tegrating the differential equations of a new set of varying elements, 

 entirely distinct in theory (though little differing in practice) from 

 the elements conceived by Lagrange; and having this advantage, 

 that the differentials of all the new elements for both the disturbed 

 and disturbing masses may be expressed by the coefficients of one 

 disturbing function. 



An Account of the Eruption of Mount Etna in the year 1536, from 

 an original cotemporary document, communicated in a letter to J. G. 

 Children, Esq., Secretary of the Royal Societv. By Sir Francis 

 Palgrave, K.G.H., F.R.S. 



Record Office of the Treasury, Chapter House, 

 Poets' Corner, Westminster, Jan. 14, 1835. 



Amongst various shreds and fragments of the correspondence from 

 Italy during the period that Henry VIII. was negotiating with the 

 Italian princes, is a document of a very different nature from the rest, 

 being an extract from a letter written by the Barone di Burgis, dated 

 at Palermo, 10th of April 1536, and giving an accountof the then re- 

 cent eruption of Mount Etna. 



" Die xxiij. Martii, M. D. xxxvi., nocte, Mons Ethna qui nunc 

 Mongibellus vocatur ; facto, orientem versus, ostio, emisit materiam 

 igneam, quae ad instar fluminis vagata est per octo miliaria in longi- 

 tudine, et per unum miliare in latitudine; ejus vero altitudo erat 

 palmarum duodecim. Eadem nocte ignis extinctus est, et ubique 

 remansit nigra materies praedictae altitudinis duodecim palmarum. Ig- 

 nis totam liquefecit nivem, quae ad instar rapidi torrentis tanto impetu 

 defluit, ut domus, arbores, et quicquid obviam esset secum traheret. 



" Sequentibusautem diebus scissa sunt aliaostia numero tredecim, 

 quae miro strepitu ignem evomebant ad instar bombardarum j longe- 

 que ab his per unum miliare cadebant ingentia saxa, quorum aliquot 

 judicata sunt ponderis ultra quindecim cantanorum. Post strepitum 

 sequebatur odor sulphureus per aliquot miliaria in locis circumvicinis. 

 Tantus erat impetus hujus igneae materiei, ut arbores prostraret et 

 evelleret antequam eas tangerat, sique veterem materiem incendiorum 

 praeteritorum saeculorum, offendebat, earn denuo incendebat. 



" Ex quolibet ostio profluebant amplissimi rivi, qui aliquo in loco 

 sua latitudine unum miliare occupabant, erantque altitudine duodecim 

 palmarum. 



" Duravit hie ignis per sex dies, et singula quaque nocte aspicieba- 

 tur in cacumine montis, ignis j die vero, fumus. 



<< Sed cognosci nequibat quern faceret effectum, quia illuc ascen- 

 dere non licebat propter relictam materiem incendii." 



